Rex Thorpe

Professor Rex Thorpe

Professor of Chemical Engineering
MEng, PhD, FIChemE, CEng, FHEA
+44 (0)1483 689270
20 BC 02
9 - 5.30

Academic and research departments

Department of Chemical and Process Engineering.


University roles and responsibilities

  • Undergraduate Admissions Tutor

    Previous roles

    2008 - 2015
    Head of Chemical and Process Engineering
    University of Surrey


    Research interests


    Postgraduate research supervision

    Completed postgraduate research projects I have supervised

    My teaching

    Courses I teach on


    My publications


    Gear M, J Sadhukhan, R Thorpe, R Clift, J Seville, M Keast (2018) A life cycle assessment data analysis toolkit for the design of novel processes - a case study for a thermal cracking process for mixed plastic waste, Journal of Cleaner Production, 180, 735-747.

    Mauro Lafratta, Rex B. Thorpe, Sabeha K. Ouki, Achame Shana, Eve Germain, Mark Willcocks, Jacquetta Lee (2020)Dynamic biogas production from anaerobic digestion of sewage sludge for on-demand electricity generation, In: Bioresource Technology310123415 Elsevier

    Oliver Crossley, Rex Thorpe, Dominik Peus, Judy Lee (2020)Phosphorus recovery from process waste water made by the hydrothermal carbonisation of spent coffee grounds, In: Bioresource Technology301122664 Elsevier


    Matthew Gear, Jhuma Sadhukhan, Rex Thorpe, Roland Clift, Jonathan Seville, M Keast (2018)A life cycle assessment data analysis toolkit for the design of novel processes - A case study for a thermal cracking process for mixed plastic waste, In: Journal of Cleaner Production180pp. 735-747 Elsevier
    The earlier in the development of a process a design change is made, the lower the cost and the higher the impact on the final performance. This applies equally to environmental and technical performance, but in practice the environmental aspects often receive less attention. To maximise sustainability, it is important to review all of these aspects through each stage, not just after the design. Tools that integrate environmental goals into the design process would enable the design of more environmentally friendly processes at a lower cost. This paper brings together approaches based on Life Cycle Assessment (LCA) including comparisons of design changes, hotspot analysis, identification of key impact categories, environmental break-even analysis, and decision analysis using ternary diagrams that give detailed guidance for design while not requiring high quality data. The tools include hotspot analysis to reveal which unit operations dominate the impacts and therefore should be the focus of further detailed process development. This approach enables the best variants to be identified so that the basic design can be improved to reduce all significant environmental impacts. The tools are illustrated by a case study on the development of a novel process with several variants: thermal cracking of mixed plastic waste to produce a heavy hydrocarbon product that can displace crude oil, naphtha, or refinery wax or be used as a fuel. The results justified continuing with the development by confirming that the novel process is likely to be a better environmental option than landfill or incineration. The general approach embodied in the toolkit should be applicable in the development of any new process, particularly one producing multiple products.
    It is well accepted that the technical, financial and environmental performance of a chemical process is largely determined during design. Therefore, the development of tools that integrate environmental considerations would enable the design of more environmentally friendly processes at a lower cost. This research investigates how Life Cycle Assessment (LCA) can be applied at any stage in the design process to produce useful information for design, not just after the plant is operating, which is the norm for LCA. The tools have been applied to the development of a novel process (the RT7000): thermal cracking of mixed plastic waste to produce several hydrocarbon products with the potential to displace crude oil, naphtha, or refinery wax or be used as a fuel. To allow LCA to guide the design process, a toolkit methodology was developed including comparisons of design changes, hotspot analysis, identification of key impact categories, environmental break-even analysis, and decision analysis using ternary diagrams. The results of applying these tools justified continuing with the development by confirming that the novel process is likely to be a better environmental option than landfill or incineration. At the later stages of design, advanced tools such as process simulations become attractive and allow a more accurate estimation of material and energy flows. A simulation of the RT7000 in Aspen Plus® was developed that provided data for a wide range of feed compositions. The RT7000 continued to have lower environmental impact to incineration offering a saving equivalent to 969-1305 kgCO2/tonne plastic processed. It was also ascertained that variation in feed composition does influence environmental performance, but not enough to affect the outcomes of decision making. The general approaches used in this work to assess the RT7000 should be applicable to the development of any new process. Benefits and insights similar to those obtained in the case study can realistically be expected when these methodologies are applied to any new processes. Therefore the results have been published in the Journal of Cleaner Production (Gear et al., 2018)
    HB Mahood, AN Campbell, Rex Thorpe, AO Sharif (2015)A new model for the drag coefficient of a swarm of condensing vapour-liquid bubbles in a third immiscible liquid phase, In: CHEMICAL ENGINEERING SCIENCE131pp. 76-83 PERGAMON-ELSEVIER SCIENCE LTD
    A semi-analytical model for the drag coefficient of a swarm of two-phase bubbles, condensing in direct contact with an immiscible sub-cooled liquid, has been developed. The analysis used a cellular model configuration, assuming potential (but not inviscid) flow around the reference two-phase bubble in the cell. The effect of the condensation ratio within the two-phase bubbles was included using an approximate relation. The drag coefficient for a wide range of Reynolds numbers (0.1. ≤. Re. ≤. 1000) has been found using the viscous dissipation integral method, and the effect of the liquid content within the two-phase bubble or the half opening angle (β), and the system void fraction (α) were examined. The drag coefficient has been found to increase with the condensation ratio and with the void fraction of the system. The present model agrees well with previously available experimental data and theoretical predictions for single bubbles or particles.
    Co-produced water re-injection is a mature recovery technique for oil fields. Co-produced water that is not re-injected is the largest wastage stream in the oil industry. Handling, treatment and management (especially re-injection back into the reservoir) is an expensive operation. PWRI is a secondary oil recovery method with a small recovery factor in the range of 15-25% and contributes to many surface and subsurface issues, e.g., scaling and reservoir plugging, resulting in the decline of water injectivity, and thus lower oil recovery. This reduction, of course, impinges significantly on the revenue stream of major oil corporations. However, low-salinity (LowSal) water injection is an emerging method that boosts oil recovery by reducing the downsides of produced water re-injection. Using forward osmosis to produce low-salinity water for injection is a novel idea, in which the co-produced water will be the draw solution. In this concept, low-salinity water from water wells (brackish water) is used as the feed to dilute the co-produced water. The diluted co-produced water will then be re-injected as LowSal water. The obviously cheaper alternative of direct dilution of the co-produced water with the brackish water might not produce a water compatible with the oil reservoir in both ionic composition and strength. Data have been collected from different oil fields with various co-produced water and formation characteristics. Different co-produced water treatments were observed in each oil field due to differences in co-produced water chemistry. The water sample for analysis was taken at the skim tanks prior to the water injection stage. A theoretical resistance-in-series model for the forward osmosis stage is presented, which has been adapted from the literature, which incorporates the mass transfer equations, in which the boundary layer and thin-film theory for the membrane intrinsic layers are integrated. An improved shell mass transfer correlation is introduced in addition to the incorporation of a modified reflection coefficient into the resistance-in-series model. The collected data were then incorporated into the theoretical model to calculate and evaluate the forward osmosis performance and, in turn, the water chemistry before re-injection. A forward osmosis rig has been erected to use the latest hollow fibre membrane supplied by the Toyobo Company (Japan). Water and solute flux were measured to validate the model estimations. The model estimated results were at 95% confidence to the measured values. Analytical investigations (ion analysis) for the membrane filtrate at various flowrates and applied pressures were performed to determine the forward osmosis filtrate ion composition. The FO filtrate compositions were then simulated using ScaleChem studio software from OLI for scaling tendency. The software predicted a remarkable reduction in the scaling tendency in the injection water infrastructure (including the oil reservoir) and by more than 50% compared to conventional co-produced water re-injection. Parallel to the ScaleChem predictions, the FO filtrate water was experimentally investigated for scaling using the Differential Scaling Loop rig, in a third-party lab. The DSL results are in good agreement with the ScaleChem predictions. The experimental scaling tendency results show that the injection of forward osmosis filtrate has the minimum occurrence of scaling both in the surface and subsurface. This new concept to produce LowSal produced water re-injection has the potential to improve oil recovery by minimizing the oil reservoir plugging due to scaling.
    HB Mahood, AN Campbell, Rex Thorpe, AO Sharif (2015)Experimental measurements and theoretical prediction for the volumetric heat transfer coefficient of a three-phase direct contact condenser, In: International Communications in Heat and Mass Transfer66pp. 180-188
    An experimental investigation of heat exchange in a three-phase direct contact condenser was carried out using a 70-cm-high Perspex tube with a 4-cm inner diameter. The active direct contact condenser comprised 48 cm. Pentane vapour at three initial temperatures (40℃,43.5℃, and 47.5℃) and water at a constant temperature (19℃) were used as the dispersed and continuous phases, respectively, with different mass flow rate ratios. The results showed that the continuous phase outlet temperature increased with increasing mass flow rate ratio. On the contrary, the continuous phase temperature decreased with increases in the continuous mass flow rate. The initial temperature of the dispersed phase slightly affected the direct contact condenser output, which confirms a latent phase effect in this type of heat exchanger.
    H Mahood, Alasdair Campbell, Rex Thorpe, Adel Sharif (2017)Measuring the overall volumetric heat transfer coefficient in a vapour-liquid-liquid three-phase direct contact heat exchanger, In: Heat Transfer Engineering39(3)pp. 208-216 Taylor & Francis
    An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct contact condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct contact condensation height. Pentane vapour at three different initial temperatures (40°C, 43.5°C and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.
    HB Mahood, AO Sharif, Rex Thorpe (2015)Transient volumetric heat transfer coefficient prediction of a three-phase direct contact condenser, In: HEAT AND MASS TRANSFER51(2)pp. 165-170 SPRINGER
    HB Mahood, AN Campbell, Rex Thorpe, AO Sharif (2015)Heat Transfer Efficiency and Capital Cost Evaluation of a Three-Phase Direct Contact Heat Exchanger for the Utilisation of Low-Grade Energy Sources, In: Energy Conversion and Management106pp. 101-109 Elsevier
    Low-grade energy cycles for power generation require efficient heat transfer equipment. Using a three-phase direct contact heat exchanger instead of a surface type exchanger, such as a shell and tube heat exchanger, potentially makes the process more efficient and economic. This is because of its ability to work with a very low temperature driving force, as well as its low cost of construction. In this study, an experimental investigation of the heat transfer efficiency, and hence cost, of a three-phase direct contact condenser has been carried out utilising a short Perspex tube of 70 cm total height and 4 cm internal diameter. Only 48 cm was used for the direct contact condensation. Pentane vapour with three different initial temperatures (40℃, 43.5℃ and 47.5℃) was contacted with water with an inlet temperature of 19℃. In line with previous studies, the ratio of the fluid flow rates was shown to have a controlling effect on the exchanger. Specifically, the heat transfer efficiency increased virtually linearly with this ratio, with higher efficiencies also being observed with higher flow 2 rates of the continuous phase. The effect of the initial temperature of the dispersed phase was shown to have a lower order impact than flow rate ratio. The capital cost of the direct contact condenser was estimated and it was found to be less than the corresponding surface condenser (shell and tube condenser) by 30 times. An optimum value of the continuous phase flow rate was observed at which the cost of the condenser is at a minimum. Keywords: Three-phase direct contact condenser, heat transfer efficiency, costing
    In the present work, for the first time, an experimental and theoretical study of the heat transfer characteristics of a bubble type three-phase direct contact condenser has been carried out. The experiments were conducted using a Perspex column of 70 cm in total height and 4 cm inner diameter, as a direct contact condenser. The active column height throughout the experiments was 48 cm. Pentane vapour at three different initial temperatures (40℃, 43.5℃ and 47.5℃), was used as the dispersed phase while tap water at a constant temperature (19℃) was used as the continuous phase. Seven different dispersed phase mass flow rates and five different continuous phase mass flow rates were tested. The experiments considered the transient temperature distribution along the direct contact condenser, the steady-state temperature distribution, the volumetric heat transfer coefficient, the heat transfer rate per unit volume and the holdup ratio. Also, the efficiency and capital cost of the direct contact condenser were estimated, and the heat transfer of the three-phase direct contact condenser during flooding was studied. Theoretical models describing the direct contact condenser were developed. These models included the transient temperature distribution, the steady-state temperature distribution and the volumetric heat transfer coefficient. These models implicitly involved new derivations for the surface heat transfer coefficient, the two-phase bubble size, the relative velocity of two-phase bubbles, the drag coefficient and the added mass of the two-phase bubble. All expressions were derived analytically except for the transient temperature distribution along the condenser which was found numerically, using MATLAB. The results showed that the mass flow rate ratio has a significant effect on the heat transfer characteristics of the condenser, while the initial temperature of the dispersed phase has only a slight effect. The models developed were fitted the experimental data well.
    HB Mahood, AO Sharif, S Al-Aibi, D Hawkins, Rex Thorpe (2014)Analytical solution and experimental measurements for temperature distribution prediction of three-phase direct-contact condenser, In: ENERGY67pp. 538-547 PERGAMON-ELSEVIER SCIENCE LTD
    HB Mahood, AN Campbell, AO Sharif, Rex Thorpe (2016)Heat Transfer Measurement in a Three-Phase Direct-Contact Condenser under Flooding Conditions, In: Applied Thermal Engineering Elsevier
    The transient temperature distribution and volumetric heat transfer coefficient during the 16 inception of flooding in a three-phase bubble type direct contact condenser have been 17 experimentally investigated. The flooding mechanism and the factors affecting the onset of 18 flooding of the three-phase direct contact column are not considered. A short Perspex column 19 of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. 20 Pentane vapour with initial temperatures of 40°C, 43.5°C and 47.5℃ was the dispersed phase 21 and tap water at a constant temperature (19℃) was the continuous phase. Only 48 cm of the 22 column was used as the active height and different mass flow rates of both phases were used. 23 The experimental results showed that the instantaneous temperature distribution along the 24 direct contact column tends to be uniform when the direct contact column is working under 25 flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the 26 dispersed mass flow rate is increased towards the flooding limit and remains constant along 27 the column height. In addition, the dispersed phase mass flow rate that leads to flooding 28 increased with increasing mass flow rate of the continuous phase. The initial temperature of 29 the dispersed phase did not have a considerable effect on the flooding inception limit under 30 the present experimental conditions
    Hameed B. Mahood, Alasdair Campbell, Ali Sh. Baqir, Adel Sharif, Rex Thorpe (2017)Convective Heat Transfer Measurements in a Vapour-Liquid-Liquid Three-Phase Direct Contact Heat Exchanger, In: Heat and Mass Transfer54(6)pp. 1697-1705 Springer Verlag
    Energy usage is increasing around the world due to the continued development of technology, and population growth. Solar energy is a promising low-grade energy resource that can be harvested and utilised in different applications, such solar heater systems, which are used in both domestic and industrial settings. However, the implementation of an efficient energy conversion system or heat exchanger would enhance such low-grade energy processes. The direct contact heat exchanger could be the right choice due to its ability to efficiently transfer significant amounts of heat, simple design, and low cost. In this work, the heat transfer associated with the direct contact condensation of pentane vapour bubbles in a three-phase direct contact condenser is investigated experimentally. Such a condenser could be used in a cycle with a solar water heater and heat recovery systems. The experiments on the steady state operation of the three-phase direct contact condenser were carried out using a short Perspex tube of 70 cm in total height and an internal diameter of 4 cm. Only a height of 48 cm was active as the direct contact condenser. Pentane vapour, (the dispersed phase) with three different initial temperatures (40℃,43.5℃ and 47.5℃) was directly contacted with water (the continuous phase) at 19℃. The experimental results showed that the total heat transfer rate per unit volume along the direct contact condenser gradually decreased upon moving higher up the condenser. Additionally, the heat transfer rate increases with increasing mass flow rate ratio, but no significant effect on the heat transfer rate of varying the initial temperature of the dispersed phase was seen. Furthermore, both the outlet temperature of the continuous phase and the void fraction were positively correlated with the total heat transfer rate per unit volume, with no considerable effect of the initial temperature difference between the dispersed and continuous phases.
    HB Mahood, Rex Thorpe, AN Campbell, AO Sharif (2015)Effect of Various Parameters on the Temperature Measurements In a Three-Phase Direct Contact Condenser, In: International Journal of Thermal Technologies5(1)pp. 23-27
    E Daar, L King, A Nisbet, Rex Thorpe, DA Bradley (2010)Viscosity changes in hyaluronic acid: Irradiation and rheological studies, In: APPLIED RADIATION AND ISOTOPES68(4-5)pp. 746-750
    Oliver Crossley, Rex Thorpe, Dominik Peus, Judy Lee (2020)Phosphorus recovery from process waste water made by the hydrothermal carbonisation of spent coffee grounds, In: Bioresource Technology301122664 Elsevier
    This study investigates the recovery of phosphorus from the process water obtained through hydrothermal carbonisation (HTC) of a ‘wet’ biomass waste, namely spent coffee grounds. HTC was shown to liberate more than 82% of the total phosphorus in the grounds in the form of dissolved ortho-phosphate. Nanofiltration was used to concentrate the inorganic nutrients of the HTC process water, achieving a mass concentration factor of 3.9 times. The natural stoichiometry of phosphorus, magnesium and ammoniacal nitrogen in the nanofiltration retentate was favourable for struvite precipitation. 92.8% of aqueous phosphorus was recovered as struvite through simple pH adjustment, yielding a total phosphorus recovery of 75% from the feedstock spent coffee grounds.

    In general, bubble surface instabilities (herein known as bubble transience), increase sonochemical (SC) processes and decrease processes, such as sonoluminescence (SL), that require higher collapse intensities. However, there is a limited understanding of how SL and SC processes are impacted by bubble transience in a practical sense. Thus, research and experimentation was based on the variation of parameters that would affect transience which, in turn, would determine ultrasound process outcomes.

    Firstly, the ultrasonic system was characterised using SL, and the SC processes of sonochemiluminescence (SCL) and potassium iodide (KI) dosimetry. Frequencies of 20 kHz (ultrasonic horn) and 44, 300 and 1000 kHz (ultrasonic plates) were used with applied flow rates of 0, 24, 228 and 626 mL / min. These frequency and flow settings were used throughout the work unless otherwise specified. The SCL and dosimetry showed disparities throughout, attributed to changes in the energy of collapse, fragmentation and oxygen concentration / solvated electrons. At low frequency, SCL and dosimetry increased under more transient collapse conditions, as measured by the minimisation of the more pyrolytic process of SL. Here, it was theorised that bubble fragmentation and radical transfer to solution, favoured dosimetry over SCL. Further, where SL and SCL activity overlapped they showed the expected reciprocal relationship of decrease / increase with bubble transience, but where activity differed there was poor correlation.

    Then, the impact of bubble transience on the intensity of collapse on SL from KI solutions (0.1, 1 and 2 M) under fluid flow and stabilised conditions were studied. At 20 kHz (horn) and 44 kHz (plate), flow reduced bubble coalescence and clustering, increasing SL intensity. However, for the 44 kHz system, at higher flow rates, bubble transience could also reduce SL. With an increase in KI concentration, at low frequency (44 kHz), localised activity could be expanded, then at higher frequencies (300 and 1000 kHz), SL activity increased towards the transducer. This indicated reduced attenuation of the sound field, attributed to a reduction in bubble size / clustering with the salt. An increase in standing wave formations (plate) or activity at the horn tip, with power (20 kHz), stabilisation (44 and 300 kHz) or flow (1000 kHz), allowed flow and salt concentration to reduce bubble coalescence / clustering in those regions. This effect could negate a decrease in SL, with increase in KI concentration at low frequency, as previously observed by other authors.

    To understand how bubble transience affected SC and SL processes, the degradation of phenol and SL from phenol under fluid flow (and stabilised) conditions was investigated. Flow could augment phenol degradation at all frequencies. For the 20 kHz (horn) and 300 kHz systems, phenol degradation correlated with iodide dosimetry which suggested an oxidative process, however, 44 and 1000 kHz showed poor correlation. At 44 kHz, degradation was hypothesised to occur inside the bubbles under transient (flow) bubble conditions, as indicated by SL quenching when degradation was maximised. This was theorised to occur via nanodroplet / rectified diffusion mechanisms. At 1000 kHz the disparity between phenol degradation and iodide dosimetry was attributed to a reduction in collapse intensity and fragmentation which affected the reaction schemes. Here, the fragmentation conditions with flow were not sufficient to increase the dosimetry, whereas for degradation, fragmentation was less influential. SL analysis for higher concentrations of phenol (horn and plate transducers) showed that intensity could be increased with flow / stabilisation. This was attributed a reduction in coalescence / clustering by both flow and the surface properties of the phenol.

    The methods of SC and SL characterisation were then applied to further understand the ultrasonic degradation of perfluorooctanesulfonic acid (PFOS). PFOS is a surfactant that will reside more readily at the bubbles surface than phenol. Therefore, effects at the bubble surface and bubble population may play more of a role. Plate transducers at frequencies of 44, 400, 500 and 1000 kHz, and a single input power (40 W) provided a range of SC and SL characteristics to measure against PFOS degradation. At higher frequencies, degradation of up to 96.9% (400 kHz) of the initial PFOS value was achieved, with similar, but slightly lower, degradations at 300 and 1000 kHz. However, at 44 kHz no degradation was observed. Therefore, an increase in the number of bubbles and bubble surface availability at the higher frequencies was favourable to the process, and further degradation did not take place inside the bubbles at low frequency. Comparison to SL and SC processes indicated that pyrolysis at the bubble surface may not be the only degradation mechanism, rather solvated electrons at the bubble surface likely contribute to PFOS degradation.

    Overall, bubble transience increased by fluid flow was, generally, favourable to SC processes. Also, flow could increase SL, in unison with the intrinsic properties of solutes (and stabilisation), by reducing coalescence / clustering in reinforced high pressure regions. Increases in bubble transience were also hypothesised to influence reaction pathways, bubble fragmentation or nanodroplet / diffusion mechanisms, more favourable to some SC processes than others. Then, the comparison of SC and SL to PFOS degradation suggested that solvated electrons may be contributing to bubble surface SC reactions. By the understanding of the fundamentals of ultrasound cavitation and bubble characteristics, both SL and SC processes have been augmented and new insights have been realised.

    Behzad Haji Mirza Beigi (2020)Odour treatment in sewage treatment works University of Surrey
    Biotrickling filtration (BTF) of malodours from Sewage Treatment Works, is investigated in detail, as the most economical and environmentally friendly air treatment option. Experimental data were produced on the removal of H2S and VOCs by a Biotrickling filter (BTF) demonstration plant, namely a SULPHUSTM, which was installed by Thames Water in late 2015. The two widely used models of Ottengraf and van den Over (1983) for BTFs were found to be inadequate with Root Mean Squared Errors (RMSE) of 22 and 4.8 mg m-3 of H2S respectively. These models are based on zero-order kinetics in the biofilm. Neither of these two existing models accounts for the possibility of diffusion limitation emerging at a point within the bed height; therefore, a novel hybrid model was developed for this possibility, which failed to improve the fit provided by the existing zero-order models. This confirms that the zero-order kinetics assumption is main source of error. The Michaelis Menten (M-M) kinetic model, predicts that zero-order is likely to be inaccurate at low pollutant concentrations when the kinetics should asymptote to fist order kinetics. However, first-order kinetics, which is found in the literature on BTFs, also fails to follow the trend of the data with RMSE of 0.36 mg m-3. A novel derivation based on the M-M kinetics is found to fit the data better the rest of the models with RMSE of 0.26 mg m-3. All models were also compared to the total VOC removal for the SULPHUSTM trial, and the M-M equation was also found to provide the best fit. In the SULPHUSTM unit used in the trials, the product of the retention time and the specific surface area was higher than typically practiced. Thus, whilst the inlet concentration reached values too high for the first-order model, the concentration in most of the bed had been reduced low enough to render the zero-order model inaccurate. The zero-order models provide a good fit to some of the laboratory H2S data by others at lower Empty Bed Retention Times (EBRT) and higher inlet concentrations than our case study. The zero order model fitting results of these data sets and the model fitting of the M-M model to our data all produced reaction rate constants of about 0.3 g/m3/s. This advance in the mathematical modelling of bio-tricking filtration has made it possible to demonstrate consistency in a seemingly disparate sets of experimental data within the biological air pollutant removal literature.
    F. Sempere, P. Winter, A. Waalkens, N. Hühnert, I. Cranshaw, B. Beigi, R. B. Thorpe (2018)Treatment of discontinuous emission of sewage sludge odours by a full scale biotrickling filter with an activated carbon polishing unit, In: Water Science and Technology77(10)pp. 2482-2490 IWA Publishing
    A SULPHUS™ biotrickling filter (BTF) and an ACTUS™ polishing activated carbon filter (ACF) were used at a wastewater treatment plant to treat 2,432 m3·h–1 of air extracted from sewage sludge processes. The project is part of Thames Water’s strategy to reduce customer odour impact and, in this case, is designed to achieve a maximum discharge concentration of 1,000 ouE·m–3. The odour and hydrogen sulphide concentration in the input air was more influenced by the operation of the sludge holding tank mixers than by ambient temperature. Phosphorous was found to be limiting the performance of the BTF during peak conditions, hence requiring additional nutrient supply. Olfactometry and pollutant measurements demonstrated that during the high rate of change of intermittent odour concentrations the ACF was required to reach compliant stack values. The two stage unit outperformed design criteria, with 139 ouE·m–3 measured after 11 months of operation. At peak conditions and even at very low temperatures, the nutrient addition increased considerably the performance of the BTF extending the time before activated carbon replacement over the one year design time. During baseline operation the BTF achieved values between 266-1,647 ouE·m–3 even during a 6 days irrigation failure of the biofilm.
    J Min, X Li, Z Gao, S Xiao, JM Smith, Rex Thorpe (2007)Experimental and CFD studies of a fluid flow in a draft-tube stirred tank, In: JOURNAL OF CHEMICAL ENGINEERING OF JAPAN40(8)pp. 630-635 SOC CHEMICAL ENG JAPAN
    JL Hau, R Ray, Rex Thorpe, A Azapagic (2008)A thermodynamic model of the outputs of gasification of solid waste, In: International Journal of Chemical Reactor Engineering6(1)ARTN A35
    Rex Thorpe (2015)Statistical analysis of the hydrodynamic forces acting on pipe bends in gas–liquid slug flow and their relation to fatigue, In: Chemical Engineering Research and Design104pp. 457-471 Elsevier
    In this paper, the resultant hydrodynamic force ( FR , where 2 2 FR  Fx  Fy ) acting on pipe bends will be discussed. A hypothesis that the peak (resultant) forces, FR, peak acting on pipe bends can be described by the normal distribution function will be tested, with the purpose of predicting the mean of the FR, peak ( FR, mean ) and the standard deviations of the FR, peak ( FR, standard deviation ) generated. This in turn allows prediction of the probability of the largest forces that occasionally occur at various flow rates. This information is vital in designing an appropriate support for the piping system, to cater the maximum force over a long period of operation. Besides, this information is also important in selecting a pipe material or material for connections suitable to withstand fatigue failure, by reference to the S-N curves of materials. In many cases, large numbers of response cycles may accumulate over the life of the structure. By knowing the force distribution, ‘cumulative damage’ can also be determined; ‘cumulative damage’ is another phenomenon that can cause fatigue, apart from the reversal maximum force.
    JA Woods, Rex Thorpe, SE Johnson (2008)Horizontal pneumatic conveying from a fluidized bed, In: CHEMICAL ENGINEERING SCIENCE63(7)pp. 1741-1760 PERGAMON-ELSEVIER SCIENCE LTD
    S Zigan, Rex Thorpe, U Tuzun, GE Gisle (2006)Air current segregation of alumina powder, In: AIChE Annual Meeting, Conference Proceedings
    This paper outlines the industrial problem of air current segregation in alumina storage silos which occurs with the handling of the feedstock alumina in aluminium plants. One significant parameter, the air extraction rate, was studied in an experimental silo which was manufactured for this purpose. The experiments conducted in small scale devices displayed the interaction between the particle flow and air current segregation. Results from these experiments show that the increase of the silo air extraction rate reduces air current segregation. The dimensional analysis method has been applied to form dimensionless groups out of the significant parameters. Five dimensionless groups were obtained which is unwieldy. To reduce the number of dimensionless groups the physical properties were lumped into the terminal velocity. This simplified approach gives three dimensionless groups. Initial experiments justify further research to establish weather the simplified approach can scale the dynamic of the flow and the degree of segregation from a small scale silo to industrial equipment.
    RJ Watson, Rex Thorpe, JF Davidson (2012)Vertical plug-flow pneumatic conveying from a fluidised bed, In: Powder Technology224pp. 155-161
    Experiments are described on the pneumatic conveying of 2.7mm alumina particles up a vertical riser of internal diameter 46.4mm or 71.4mm. The particles entered the riser from a fluidised bed, via a short horizontal pipe and a bend of radius 75mm. Measured variables included solids flow rates, air flow rates, inlet and outlet air pressures P 1 and P 2, and the pressure profile in the riser. The solids flow rate was consistent with some earlier models of similar systems, in which the plugs of packed solids move up at a velocity of about U-U mf, where U=superficial air velocity and U mf=incipient fluidising velocity. Solids-wall friction is significant and suppresses fluidisation. To model the system approximately, a conveying efficiency=(power for air compression)/(rate of gain of potential energy of solids) is defined and correlated against solids flux. It was found that the conveying efficiency tended to an asymptote just above 20%. The correlation led to a tentative design formula, Eq. (6), for predicting P 1-P 2 at a given solids flow rate. P 1-P 2 is typically between 50% and 100% of the pressure drop needed to support a column of solids of height equal to that of the riser.It was concluded that plug flow pneumatic conveying is a satisfactory technology for transporting coarse particles which cannot be conveyed in leaner regimes due to the possibility of pipeline erosion or solids attrition. © 2012 Elsevier B.V.
    R Ray, Rex Thorpe (2007)A comparison of gasification with pyrolysis for the recycling of plastic containing wastes, In: INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING5ARTN A85 BERKELEY ELECTRONIC PRESS
    Olumayowa Kajero, Rex Thorpe, Tao Chen (2016)Kriging meta-model assisted calibration of computational fluid dynamics models, In: AIChE Journal62(12)pp. 4308-4320 Wiley
    Computational fluid dynamics (CFD) is a simulation technique widely used in chemical and process engineering applications. However, computation has become a bottleneck when calibration of CFD models with experimental data (also known as model parameter estimation) is needed. In this research, the kriging meta-modelling approach (also termed Gaussian process) was coupled with expected improvement (EI) to address this challenge. A new EI measure was developed for the sum of squared errors (SSE) which conforms to a generalised chi-square distribution and hence existing normal distribution-based EI measures are not applicable. The new EI measure is to suggest the CFD model parameter to simulate with, hence minimising SSE and improving match between simulation and experiments. The usefulness of the developed method was demonstrated through a case study of a single-phase flow in both a straight-type and a convergent-divergent-type annular jet pump, where a single model parameter was calibrated with experimental data.
    Rex Thorpe, S Zigan, U Tuzun (2009)Characterisation of free-flowing particle jets into storage silos using particle image velocimetry and DEM simulations, In: Bulk Solids & Powder Science & Technology2pp. 55-60 Trans Tech Publications
    Rex Thorpe (2002)Research not flagging, In: TCE(732)pp. 70-70 INST CHEMICAL ENGINEERS
    MA Abia-Biteo Belope, Rex Thorpe (2007)Alba field three phase separator performance, In: 13th International Conference on Multiphase Production Technologypp. 399-412
    The performance of a particular type of horizontal three phase separator (bucket & weir) was evaluated on the Alba Field, situated offshore of the coast of Equatorial Guinea, by coding a set of equations for the design of the separators. Output parameters such as the oil and water residence times, liquid droplet settling/rising times, minimum lengths for gas-liquid disengagement, and holdup and surge times for the oil bucket and the water compartment, were checked regularly against max/min values for good operation. Thus it was possible to assess the likely behavior of the four Alba field separators to changes in operating variables while also comparing the results obtained from the equations with real field data for performance. The performance of the separators was fairly consistent, even though oils of varying viscosity and temperature were processed. The values of parameters at which performance deteriorated was somewhat different from those usually quoted in the literature for good operation. © BHR Group 2007 Multiphase Production Technology 13.
    Rex Thorpe (2001)Kirchhoff no proof, In: TCE(725)pp. 49-49 INST CHEMICAL ENGINEERS
    N Mills, P Pearce, J Farrow, Rex Thorpe, NF Kirkby (2013)Environmental & economic life cycle assessment of current & future sewage sludge to energy technologies., In: Waste Manag
    The UK Water Industry currently generates approximately 800GWh pa of electrical energy from sewage sludge. Traditionally energy recovery from sewage sludge features Anaerobic Digestion (AD) with biogas utilisation in combined heat and power (CHP) systems. However, the industry is evolving and a number of developments that extract more energy from sludge are either being implemented or are nearing full scale demonstration. This study compared five technology configurations: 1 - conventional AD with CHP, 2 - Thermal Hydrolysis Process (THP) AD with CHP, 3 - THP AD with bio-methane grid injection, 4 - THP AD with CHP followed by drying of digested sludge for solid fuel production, 5 - THP AD followed by drying, pyrolysis of the digested sludge and use of the both the biogas and the pyrolysis gas in a CHP. The economic and environmental Life Cycle Assessment (LCA) found that both the post AD drying options performed well but the option used to create a solid fuel to displace coal (configuration 4) was the most sustainable solution economically and environmentally, closely followed by the pyrolysis configuration (5). Application of THP improves the financial and environmental performance compared with conventional AD. Producing bio-methane for grid injection (configuration 3) is attractive financially but has the worst environmental impact of all the scenarios, suggesting that the current UK financial incentive policy for bio-methane is not driving best environmental practice. It is clear that new and improving processes and technologies are enabling significant opportunities for further energy recovery from sludge; LCA provides tools for determining the best overall options for particular situations and allows innovation resources and investment to be focused accordingly.
    K-K Tan, Rex Thorpe (2011)Onset of instability of impulsely starting rotating cylinder, In: AIP Proceedings of the Sixth International Conference on Fluid Mechanics1376pp. 104-107
    BL Tay, Rex Thorpe (2014)Hydrodynamic forces acting on pipe bends in gas-liquid slug flow, In: CHEMICAL ENGINEERING RESEARCH & DESIGN92(5)pp. 812-825 INST CHEMICAL ENGINEERS
    MR Aliff Radzuan, MA Abia-Biteo Belope, Rex Thorpe (2016)Removal of Fine Oil Droplets from Oil-in-Water Mixtures by Dissolved Air Flotation, In: Chemical Engineering Research and Design115(A)pp. 19-33
    Dissolved air flotation (DAF) is often used after a primary gravity separator to enhance the quality of wastewater, so it can be released to streams, rivers or the sea. The main aim of the DAF experiments reported here was to measure the oil droplet removal efficiency, (η) mostly in the range 15-80 μm from oil-in-water mixtures. The DAF tank used in this investigation was a scale model of real DAF unit. Two kinds of oil, vegetable and mineral and two types of water, fresh and salty were used, and four other operating parameters were varied. A droplet counting and oil-in-water measuring methods were used to estimate the η. Dimensional analysis concluded that the η in this experiment is a function of eight other dimensionless groups and the experimental data has been subjected to multivariable linear regression. The resulting correlation was found to have a root mean square error of 6.0%, but predict η outside the range zero and one. An alternative mathematical formulation was devised that cannot predict η outside the range. Regression of the data by this formulation, which had the same number of adjustable parameters as the linear regression, was successful with a lower root mean square error of 5.5%.
    K-K Tan, Rex Thorpe, Z Zhao (2011)On predicting mantle mushroom plumes, In: Geoscience Frontiers2(2)pp. 223-235
    S Zigan, Rex Thorpe, U Tuzun, GG Enstad (2007)Air current segregation of alumina powder, In: PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION24(2)pp. 124-135 WILEY-V C H VERLAG GMBH
    Rex Thorpe, N Mills, P Pearce, N kirkby (2011)The influence of heat balance on the economics of advanced anaerobic digestion proceses, In: 16th European Biosolids and Organic Resources Conference Proceedings
    Rex Thorpe, Barnaby Brampton, Simon Robson, Aurelien Perrault (2017)Investigating the effect of an alternative feedstock on the performance of sludge powered generators: developing a theoretical model and analysing trial data, In: Proceedings of The IWA Specialist Conference On Sludge Management: Sludgetech 2017 International Water Association
    Trials performed by Thames Water on a Sludge Powered Generator (SPG) have used sludge from a Thermal Hydrolysis Process (THP) as feed. Data from the trials with THP product sludge at Thames Water's Crossness SPGs was subject to data analysis by converting the trial data into flows of operating cost. Sludge is a mixture of many chemicals and these would be very time consuming to analyse for combustion performance in full detail. Therefore sludge has been simplified to a mixture of water and a single combustible chemical component (coniferyl alcohol) with the same heat of combustion as water-free sludge and roughly the right elemental analysis. This simplification enables the thermal behaviour of the combustion, including its tendency to extinguish without support fuel, to be captured. Both the simplified model and the data analysis from the trial show the THP product sludge is a viable fuel which produces a net financial benefit to the SPG’s operation.
    Z Li, Z Gao, JM Smith, Rex Thorpe (2007)Large eddy simulation of flow fields in vessels stirred by dual rushton impeller agitators, In: JOURNAL OF CHEMICAL ENGINEERING OF JAPAN40(8)pp. 684-691
    Y Bao, Z Gao, X Huang, L Shi, JM Smith, Rex Thorpe (2007)Gas-liquid dispersion with buoyant particles in a hot-sparged stirred tank, In: INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH46(20)pp. 6605-6611 AMER CHEMICAL SOC
    YY Bao, ZG Hao, ZM Gao, LT Shi, JM Smith, Rex Thorpe (2006)Gas dispersion and solid suspension in a three-phase stirred tank with multiple impellers, In: CHEMICAL ENGINEERING COMMUNICATIONS193(7)pp. 801-825 TAYLOR & FRANCIS INC
    Mauro Lafratta, Rex B. Thorpe, Sabeha K. Ouki, Achame Shana, Eve Germain, Mark Willcocks, Jacquetta Lee (2020)Dynamic biogas production from anaerobic digestion of sewage sludge for on-demand electricity generation, In: Bioresource Technology310123415 Elsevier

    The aim of this work was to study the potentials and benefits of dynamic biogas production from Anaerobic Digestion (AD) of sewage sludge. The biogas production rate was aimed to match the flexible demand for electricity generation and so appropriate feeding regimes were calculated and tested in both pilot and demonstration scale.

    The results demonstrate that flexibilization capability exists for both conventional AD and advanced AD using Thermal Hydrolysis Process (THP) as pre-treatment. Whilst the former provides lower capability, flexible biogas production was achieved by the latter, as it provides a quick response. In all scenarios, the value of the biogas converted into electricity is higher than with a steady operational regime, increasing by 3.6% on average (up to 5.0%) in conventional and by 4.8% on average (up to 7.1%) with THP. The process has proven scalable up to 18m3 digester capacity in operational conditions like those in full scale.

    YY Bao, ZM Gao, ZP Li, D Bai, JM Smith, Rex Thorpe (2008)Solid suspension in a boiling stirred tank with radial flow turbines, In: IND ENG CHEM RES47(7)pp. 2420-2427 AMER CHEMICAL SOC
    B.H.M. Beigi, R.B. Thorpe, S. Ouki, P. Winter, A. Waalkens (2019)Hydrogen Sulphide and VOC Removal in Biotrickling Filters: Comparison of Data from a Full-scale, Low-emission Unit with Kinetic Models, In: CHEMICAL ENGINEERING SCIENCE208115033 PERGAMON-ELSEVIER SCIENCE LTD

    In this paper, data is published on the removal of H2S and VOCs by a Biotrickling Filter (BTF) demonstration plant, namely a SULPHUS™, which was installed by Thames Water in late 2015. These data, along with some data already published by Sempere et al. (2018), were compared to the predictions of a number of existing and novel models for the removal of a single pollutant by a biofilm.

    The two widely used models of Ottengraf and van den Over (1983) were found to be inadequate with sum of squares of errors of 11 and 41 mg2m-6 respectively. These models are based on zero-order kinetics in the biofilm which according to the M-M kinetic model, are likely to be inaccurate at low pollutant concentration. The odour control unit was designed to produce low emission levels of less than 1 ppmv of H2S, rendering the zero-order assumption unlikely to be accurate. A model based on first-order kinetics, which also has some support in the literature, was found to be a better, but not a good, fit to the data with a sum of squares of errors of 4.7 mg2m-6. A novel model for the BTF based on M-M kinetics was found to be a good fit to the shape of the data with the lowest sum of squares of errors of 2.5 mg2m-6. This novel M-M model was also identified as the best fit for VOC data from the same unit. Other publications support the M-M approach with a product of saturation constant and Henry’s Law constant of about 50 mg m-3, which is equivalent to an H2S level in the gas phase of about 40 ppmv. Broad agreement was found between the SULPHUS™, experiments and data in the literature for other BTFs destroying H2S under the zero-order regime, at V_max value of about 0.3 g/m3/s. This paper represents an attempt to harmonise a literature that was previously disparate, which has not previously been attempted.

    EH van der Meer, Rex Thorpe, JF Davidson (2000)Flow Patterns in the Square Cross-Section Riser of a Circulating Fluidized Bed and the Effect of Riser Exit Design, In: Chemical Engineering Science55pp. 4079-4099
    OT Kajero, Rex Thorpe, Y Yao, DSH Wong, Tao Chen (2017)Meta-model based calibration and sensitivity studies of CFD simulation of jet pumps, In: Chemical Engineering & Technology40(9)pp. 1674-1684 Wiley
    Calibration and sensitivity studies in the computational fluid dynamics (CFD) simulation of process equipment such as the annular jet pump are useful for design, analysis and optimisation. The use of CFD for such purposes is computationally intensive. Hence, in this study, an alternative approach using kriging-based meta-models was utilised. Calibration via the adjustment of two turbulent model parameters, C_μ and C_2ε, and likewise two parameters in the simulation correlation for C_μ was considered; while sensitivity studies were based on C_μ as input. The meta-model based calibration aids exploration of different parameter combinations. Computational time was also reduced with kriging-assisted sensitivity studies which explored effect of different C_μ values on pressure distribution.
    AT Harris, JF Davidson, Rex Thorpe (2002)The Prediction of Particle Cluster Properties in the Near Wall Region of a Vertical Riser, In: Powder Technology127pp. 128-143
    The UK water industry has huge, but as yet under-developed, potential to generate sustainable energy from the main by-product created in the treatment of wastewater. Sewage sludge is an energy rich sustainable biomass resource with a similar calorific value to woodchip. Until recently, technologies and processes for further energy recovery have not been efficient or viable for large-scale use, but this research has shown that developments and innovations are now available and can realistically be brought into use. Using a combination of detailed techno-economic analysis and data from several large scale demonstration plants this research has shown that the renewable energy produced from sewage sludge in the UK could be significantly increased. A typical conventional AD site will achieve 15% electrical conversion efficiency; this can be improved to 20% with the Thermal Hydrolysis Process (THP). Second generation THP developed during the project could boost recovery to 23% with other benefits such as reduced support fuel requirements and sludge transport volumes. By combining THP, sustainable thermal drying and pyrolysis, gross conversion efficiencies of 34% to electricity are achievable. All of the scenarios developed by the project have been proven to environmentally & economically sustainable and have been demonstrated at a large scale as part of this project. A UK wide study in conjunction the Department of Energy & Climate Change showed that an economic deployment across the UK of second generation THP, followed by drying and pyrolysis, could generate to 2,216GWh or an additional 1,310GWh pa of renewable electricity from sewage sludge.
    An experimental investigation was conducted to study the conversion of waste plastics and single polymers into high quality oils through the pyrolysis process at elevated temperatures that haven’t been investigated before. Furthermore, the utilisation of the produced pure oils in a diesel engine for power generation was explored, which is a novelty of this research. In addition, a longevity test was carried out in the diesel engine with a high blend of pyrolysis oil to diesel in order to understand the long-term effects of the oil in the engine performance characteristics and components. In order to improve the engine’s performance and increase the operational life of the engine, different approaches (such as the injection timing modification and fuel additive addition) were studied. Another novelty of this research is the investigation of the macroscopic spray characteristics of the plastics pyrolysis oil in a constant volume vessel. The effect of the pyrolysis temperature on the produced yields and oils quality was also explored for a mixture of plastics and different pure polymers (such as styrene butadiene, polyethylene terephthalate, ethylene-vinyl acetate, polyethylene and polypropylene) separately. An important finding of this research is that the pyrolysis of polyethylene terephthalate at high temperatures results in the production of only gas and char (no liquid) and pyrolysis plant failures. Finally, the best pyrolysis oil quality and diesel engine performance were acquired from the oil that was produced from the pyrolysis of low density polyethylene, while the rest of the oils produced from the pyrolysis of ethylene-vinyl acetate and polypropylene generated acceptable diesel engine performances.
    The release of volatile organic compounds to the atmosphere is harmful to human health and the environment. The printing industry is one of the highest contributors to VOC emissions in the UK. According to the Solvent Emissions Directive (1999), only 30 % (by weight) or less of solvents used in the printing industry can be released into the atmosphere as emissions; this is proving to be a challenge to the industry. Thus, the aim of this project is to develop and test a complete demonstration scale capture and regeneration system capable of reusing both, the adsorbent and the adsorbed VOC (in this case IPA). A prototype adsorber was built and tested at a lithographic printing company for the purpose of capturing the isopropanol (IPA) emissions, under industrial conditions. The prototype itself consisted of an extractor pipe and an adsorbent cartridge placed inside a vacuum cleaner. Adsorption was carried out by drawing in air from the printing machines where vapour emitted from the dampening solution (which comprised of about 10% by vol IPA and 90% by vol water) was concentrated. Three trials of varying inlet concentrations with an adsorbent Dowex Optipore V503 (Dow) and a one trial with activated carbon (AC), was carried out at the printing facility. The time taken until the start of breakthrough was approximately 86 minutes and 250 minutes (of printing time) for Dow and AC respectively. Results showed that, until the start of breakthrough, all of the IPA entering the bed had been captured by both adsorbents. Of the material captured on the adsorbent, the percentage that was IPA for Dow was 66 wt% to 80 wt% and the IPA percentage that was captured on AC was 54 wt%. The rest of the captured material on the adsorbents was found to be water. A higher IPA loading, however, was evident for AC as compared to Dow. Results on microwave (MW) regenerating the two adsorbents showed that maximum regeneration of 88% for Dow and 97% for AC occurred after 12 and 13.5 minutes of microwave irradiation respectively. Tiny flashes of light across and within the whole AC bed were evident frequently during the initial stages of MW regeneration. Thus, in terms of safety, the existence of tiny sparks during AC regeneration indicates that Dow is the safer of the two adsorbents. Fractional regeneration of Dow showed that maximum IPA content was found in the regenerate collected between the 6th and 9th minute while the lowest IPA content was found between 0 and 3 minutes. For AC, the percentage of IPA in the regenerate was also found to increase with irradiation time. An attempt was made to model the process. The first step was to obtain the pure adsorption isotherms at 298 K using an Intelligent Gravimetric Analyser (IGA). For the AC and Dow adsorbents, the Toth and the CIMF model fitted extremely well to the pure IPA and water isotherms respectively. The mixture isotherms were described by the virial equation. The results from the mixture experiments involving Dow showed ideal adsorption of the mixture; AC showed highly non-ideal behaviour. A mathematical model (compiled on Matlab), which incorporated the co-adsorption isotherms, was used to predict breakthrough times during fixed-bed adsorption. This model was able to predict breakthrough data for Dow fairly accurately. An economic analysis was conducted which shows that AC is the cheaper of the two adsorbents to use, subject to safety considerations. Overall, a system that captures and regenerates the IPA from the print works had been successfully developed and tested. Microwave regeneration was found to be favourable for both adsorbents since, no loss in adsorbent capacity was found after exposure to microwave radiation. On comparing the two adsorbents, Dow was found to capture a higher percentage of IPA than water as compared to AC. However, with regards to economic viability, AC was found to be the more economic adsorbent.
    Global consumption for confectionery products are growing and is exerting enormous pressures on confectionery supply chains across the world to efficiently utilise natural resources towards becoming environmentally sustainable. However, there are a disparate range of studies investigating the environmental impacts of confectionery products, and more importantly how to improve environmental sustainability performance. In this thesis, the aim was to improve knowledge of opportunities for reducing environmental impact in confectionery manufacturing – from factory to supply chain – by developing methodological tools based on heat integration and Life Cycle Assessment (LCA). A range of novel methodologies were developed to advance heat integration and LCA knowledge, including (1) a heat integration framework combining direct and indirect heat exchange from zonal to multiple zones, possibly incorporating heat pump technology to enhance low grade heat recovery; (2) methodologies for systematically improving Life Cycle Inventory (LCI) data based on the role of multinational companies and for conducting effective LCA for confectionery products; and (3) a methodology to assess and quantify the environmental life cycle impacts of multi-product food factories. These methodologies have been applied at a multi-product confectionery factory, which has revealed significant findings: (1) combining direct and indirect heat integration from zonal to multiple zones can reduce factory energy by 4.04–6.05%, (2) heat pump technology can reduce factory energy by up to 29.2% but imposes design complexity and long economic paybacks up to 6.62 years, (3) fine bakery ware products on average was found to have the highest aggregated environmental life cycle impacts (higher than chocolate products by 7.1%, milk-based products by 18%, and sugar by 51.9%), and (4) combined improvement strategies of 50% energy reduction with 100% renewable energy, zero food waste to landfill (inc. 50% food waste reduction), and raw material changes to lower impacts can potentially reduce: Global Warming Potential by 65.82%, water depletion by 43.02%, abiotic depletion potential by 20.66%, land use by 17.45% and ecosystem quality by 7.24%. Overall, this research has culminated in several contributions to knowledge which substantially increases understanding of how to improve the environmental sustainability of confectionery manufacturing across the product, factory and supply chain level. The research will serve as a guide for future improvements, research and policies of confectionery manufacturers, supply chain actors, policy makers, and research institutes.
    Dissolved air flotation (DAF) is a separation technique, often used after a primary gravity separator to enhance the quality of the wastewater, so it can be released to streams, rivers, and the sea in a manner not to violate the environment. DAF works by removing oil droplets from oil-in-water mixtures by air bubbles of an average diameter of 50 μm with a standard deviation of 5.5 μm. The air bubbles used in these experiments were generated as a result of rapid pressure reduction of water saturated with air when it released from the bottom of the DAF tank. The main aim of the DAF experiments reported here was to measure the removal efficiency of oil droplet mostly in a diameter range between 15 and 80 μm that were created using a static mixer. The DAF tank located at the University of Surrey was a scale model of existing DAF unit used by Thames Water plc. The effects of seven operating parameters that are believed to affect the performance of DAF were investigated. The operating parameters consist of inlet oil concentration, air saturator pressure, temperature, the salinity of continuous phase, type of oil, flow rate of the mixture and coagulant dosage. Two independent analysis methods were used to estimate the removal efficiency of oil droplet. They are a droplet counting and an oil-in-water measuring methods. The droplet counting method used a Coulter Counter that provided numbers of oil droplet passed through the aperture based on the selected size range. The oil-in-water measuring method used an ultraviolet and visible spectroscopy (UV-Vis), which the removal efficiencies were estimated from the absorbance values that were measured at the optimum wavelength of 400 nm. The analyses done with these two methods found that the inlet oil concentration and flow rate of the mixture into DAF tank were inversely proportional to the oil droplet removal efficiency. The other parameters such as saturator pressure, temperature, water salinity and alum dosage were directly proportional to the oil droplet removal efficiency. Vegetable oil, which has larger spreading coefficient than lamp oil obtained a better oil droplet removal efficiency. Coulter Counter showed that a better removal efficiency for vegetable oil obtained at larger oil droplet ranges size, 50μm and above. This was because the oil droplets were removed by gravity and enhanced by air bubbles. Contrary to lamp oil, which the worst removal efficiency was obtained at larger size ranges due to the coalescence of oil droplets. Results from these experiments were used to obtain a correlation that can predict removal efficiency. This was done by performing dimensional analysis. It was carried out using Buckingham Pi and scaling methods. It involved with the identification of two non-dimension and nine dimensional parameters. The dimensional analysis concluded that the removal efficiency is a function of eight other dimensionless groups, which are ratio of inlet oil and mixture flow rate
    Computational fluid dynamics (CFD) is a computer-based analysis of the dynamics of fluid flow, and it is widely used in chemical and process engineering applications. However, computation usually becomes a herculean task when calibration of the CFD models with experimental data or sensitivity analysis of the output relative to the inputs is required. This is due to the simulation process being highly computationally intensive, often requiring a large number of simulation runs, with a single simulation run taking hours or days to be completed. Hence, in this research project, the kriging meta-modelling method was coupled with expected improvement (EI) global optimisation approach to address the CFD model calibration challenge. In addition, a kriging meta-model based sensitivity analysis technique was implemented to study the model parameter input-output relationship. A novel EI measure was developed for the sum of squared errors (SSE) which conforms to a generalised chi-square distribution, where existing normal distribution-based EI measures are not applicable. This novel EI measure suggested the values of CFD model parameters to simulate with, hence minimising SSE and improving the match between simulation and experiments. To test the proposed methodology, a non-CFD numerical simulation case of the semi-batch reactor was considered as a case study which confirmed a saving in computational time, and an improvement of the simulation model with the actual plant data. The usefulness of the developed method has been subsequently demonstrated through a CFD case study of a single-phase flow in both a straight type and convergent-divergent type annular jet pump, where both a single turbulent model parameter, C_μ and two turbulent model parameters, C_μ and C_2ε where considered for calibration. Sensitivity analysis was subsequently based on C_μ as the input parameter. In calibration using both single and two model parameters, a significant improvement in the agreement with experimental data was obtained. The novel method gave a significant reduction in simulation computational time as compared to traditional CFD. A new correlation was proposed relating C_μ to the flow ratio, which could serve as a guide for future simulations. The meta-model based calibration aids exploration of different parameter combinations which would have been computationally challenging using CFD. In addition, computational time was significantly reduced with kriging-assisted sensitivity analysis studies which explored effect of different C_μ values on the output, the pressure coefficient. The numerical simulation case of the semi-batch reactor was also used as a basis of comparison between the previous EI measure and the newly proposed EI measure, which overall revealed that the latter gave a significant improvement at fewer number of simulation runs as compared to the former. The research studies carried out has hence been able to propose and successfully demonstrate the use of a novel methodology for faster calibration and sensitivity analysis studies of computational fluid dynamics simulations. This is essential in the design, analysis and optimisation of chemical and process engineering systems.