Combined heating refrigeration and power system in food industry

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1 Combined heating refrigeration and power system in food industry N. Sugiartha* 1, I. Chaer 2, D. Marriott 3 and S. A. Tassou 1 The paper describes an analysis of the application of a combined heating, refrigeration and power (CHRP) system to the chilled food industry from the perspective of energy, economic and environmental factors. It is based on theoretical and practical findings from a CHRP research project at Brunel University. The CHRP test facility employs an 80 kw e modular microgas turbine producing electrical and thermal energy for process and site use with excess heat converted into refrigeration via a 12 kw c thermally driven low temperature absorption refrigeration unit. A 1000 kg h 21 chilled dairy product plant has been considered for the analysis. The plant has energy demand of 52?5 kw e for electrical power, 36 kw th for process heating and 55 kw c for process cooling. For the plant selected, the use of the CHRP system can provide annual primary energy savings of 27%, payback time of 3?7 years and CO 2 emission savings of 76 t per annum based on utilisation of one unit of microgas turbine and five units of absorption chillers. Keywords: Energy efficiency, Combined heating refrigeration and power, Microgas turbine, Chilled food industry List of symbols Subscript c cooling e electrical f fuel th thermal Introduction The food industry is a major user of energy, accounting for nearly 100 TWh per annum, equivalent to 11% of the UK energy consumption by business, and a major contributor to the UK carbon emissions, with 7?9 million tonnes of carbon per year. 1 Additionally the industry accounts for a significant source of waste generation, accounting for about 10% of the industrial and commercial waste stream and of particular importance for certain priority waste streams, notably packaging. Meanwhile, the greenhouse impact in terms of global warming potential was estimated in the range of 22 to 31% from the total emissions. Within this range, meat and meat products and dairy products contribute 4 12% and 2 4% respectively. 2 The food industry has a demand for heating, electrical power and cooling or refrigeration during the process. The separate plants are normally employed, which consists of boiler plant producing low and high pressure hot water or steam for process and space heating, 1 School of Engineering and Design, Brunel University, Uxbridge, Middlesex, UB8 3PH, UK 2 Department of Engineering Systems, London South Bank University, 90 London Road, SE1 6LN, UK 3 Doug Marriott Associates, Kent, UK *Corresponding author, nyoman.sugiartha@brunel.ac.uk vapour compression refrigeration plant for air conditioning and refrigeration, and electrical power supply from the National grid for refrigeration systems, lighting and ancillary equipments. Technology for simultaneous generation of heating, refrigeration and electrical power as otherwise known as trigeneration or combined heating, refrigeration and power (CHRP) is considered as a potential excellent method to reduce energy consumption as well as environmental impact and to improve energy system efficiency. 3 The main objective of this paper is to assess an opportunity for reducing the energy utility costs and environmental impact and improving significantly the overall system s energy efficiency, relating to an integrated refrigerated chilled food manufacturing process by the use of a trigeneration process using CHRP. UK energy policy The Energy White Paper published in 2003 and the associated Energy Review published in July 2006 calls for a reduction in CO 2 emissions by 60% from the 1990 level by the year ,5 A reduction of 60% in 60 years or 1% per annum calls for a radical review of energy utility management and use in order to meet the legislative controls, which are being introduced and the associated future controls, which will be implemented and the inevitable increase in energy prices which clearly will go hand in hand with such controls. The energy situation in the UK is a particularly significant issue to be considered and particularly in the food industry. Because energy is becoming scarce and a dependency on imported gas and liquid natural gas is inevitably going to increase prices with time, where planning for renewable energy will not keep pace with ß 2008 Energy Institute Published by Maney on behalf of the Institute Received 15 February 2008; accepted 23 March 2008 DOI / X Journal of the Energy Institute 2008 VOL 81 NO 4 185

2 current industrial demand, the food sector is bound to attract attention in terms of legislation. In the foreseeable future, energy prices will increase and these are likely to be significant in the current investment cycle. The high energy use in food production is bound to draw attention to that sector and one can expect incentives and/or penalties if efficiency initiatives are not implemented. Intermittent price volatility will be apparent due to weather, distribution reliability, market energy fluctuations as well as political volatility from time to time, which can be expected with certainty. If one is able to install new utility plant and equipment with improved efficiencies, which can meet the energy policy demands by effectively stepping forward a couple of decades, then such a strategy will ensure a like for like overhead advantage over competitors who have not invested wisely, while, at the same time, addressing to some extent the responsibility we all face to reduce demand on a finite resource. The use of gas as the primary energy for a utility has an advantage in the longer term. With capability to purchase the fuel on an interruptible supply, by using a gas compression plant to cover for the contract outage, there is a possibility to negotiate lower gas prices on preferred tariffs. The recovery of the capital investment for the compression plant or alternatively contracting to purchase gas on a supply basis, with the integral compression plant supplied as part of the utilities distribution infrastructure, offers potentially attractive scenarios, which are not as yet evident. The food industry is a producer of waste and as energy from waste becomes commercially viable then suitable applications in food processing will also become the subject of further consideration using waste gasification for example to power trigeneration, in turn avoiding expensive land fill taxation and generally unacceptable practices of disposing of potentially polluting waste. UK energy supply The UK energy mix is changing rapidly and with the future of investment in generation plant not clearly defined, together with existing nuclear plant moving closer to decommissioning in the next decade, then production of electricity is clearly under pressure to meet demand to maintain supply from the main grid. The application of thermal power stations supplying the grid, taking into account the latest efficient plant will result in power being delivered currently to the consumer at as low as 38% electrical efficiency with some 7?5% of that figure lost in distribution. 6,7 Those losses are invariably not recoverable. Food processing is substantially a thermal process and energy efficiency will by necessity have to be much higher to reduce food industry overheads. For these and other reasons the UK government regulators and industry are moving towards embedded generation, where there is an ability to capture the otherwise lost energy dissipated by power stations. The drive for renewable resources connected to local energy demand, which allows for all the surplus to be exported through the national grid is also causing future concern for grid stability and reliability, so there is clearly an urgent need to address utility services using improved thermally efficient embedded power. Drivers for improvement in refrigeration systems Chilled food processing plant invariably has a coincident demand for heat, refrigeration and electrical energy and, provided the demand for energy is in phase and in appropriate quantum to be produced, then trigeneration in terms of CHRP becomes a serious option to consider in the selection of the energy supply. In general, the food production industry has a consistent and constant demand for energy while running plant and that is largely independent of the time of year: summer process demand will not be significantly different from that in winter. There is a need for coincident power and heat to ensure combined heat and power (CHP) is viable Trigeneration has in the past been integrated with absorption coolers in a number of industrial and commercial applications, particularly in air conditioning have been reported, but as yet have not been widely used in the smaller scale size ((300 kw c refrigeration duty) in food production applications. 13 Research work Research at Brunel University, supported by a number of industrial partners and funded by Department of Environment, Food and Rural Affairs (DEFRA) is aimed at the development of a trigeneration system for low temperature refrigeration applications. The work has concentrated on the application of microgas turbine (MGT) based trigeneration systems to supermarkets in the UK using component efficiency data obtained from laboratory investigations. There is a close parallel between the above application and chilled food processing. Experimental investigations The project involved the design and construction of a trigeneration test facility at Brunel University (see Fig. 1). This trigeneration test facility incorporates a CHP module, an absorption refrigeration system module and a refrigeration load module with comprehensively instrumented controls to facilitate detailed investigations of design and control aspects of the trigeneration systems to be carried out at controlled conditions. This will be useful not only for food engineering but also other combined heat and power and trigeneration applications. Microgas turbine Figure 2 shows various components of Bowman MGT based CHP system with the following specifications: (i) type: recuperative cycle, constant speed around rev min 21 (ii) electrical output: 80 kw e (full load) (iii) exhaust gas temperature: 260 to 413uC (depending on level of recuperation) (iv) exhaust mass flow rate: 0?831 to 0?837 kg s 21 (v) thermal output: 150 to 288 kw th The level of recuperation on the MGT unit can be changed through a bypass valve that allows some of the gas to bypass the recuperator. The level of recuperation will influence the exhaust gas temperature available for heat recovery and the electrical generation efficiency of the system. Maximum recuperation will lead to 186 Journal of the Energy Institute 2008 VOL 81 NO 4

1 Schematic diagram of CHRP test facility maximum electrical power output and minimum thermal output and no recuperation will lead to minimum electrical power output (electrical generation

It can be seen that the electrical generation efficiency of the turbine increases with power output of the turbine.

Absorption chiller The absorption unit employed is a gas fired Robur ammonia water chiller (ACF-60LB-model) as shown in Fig.

3 1 Schematic diagram of CHRP test facility maximum electrical power output and minimum thermal output and no recuperation will lead to minimum electrical power output (electrical generation efficiency of around 16%) but maximum thermal output. The MGT unit has been installed and tested in the laboratory and Fig. 3 shows some of the characteristics. It can be seen that the electrical generation efficiency of the turbine increases with power output of the turbine. For the conditions tested, the efficiency was found to be 28 % at the maximum electrical output of 80 kw e. Absorption chiller The absorption unit employed is a gas fired Robur ammonia water chiller (ACF-60LB-model) as shown in Fig. 4, which of specified cooling capacity of 12 kw c at ambient temperature of 35uC and chilled water inlet and outlet temperatures of 0 and 25uC. 15 The unit was installed and tested over a range of brine flow 3 Variation of electrical generation efficiency with power output (net calorific value of fuel: 34?9 MJm 23 ) 2 Bowman TG80RC-G MGT CHP system 14 4 Robur low temperature absorption chiller 15 Journal of the Energy Institute 2008 VOL 81 NO 4 187

5 Refrigeration capacity and COP versus brine delivery temperature for two ambient ranges temperatures between 3 and 211uC at constant brine flow rate of 0?64 kg s 21.

4 5 Refrigeration capacity and COP versus brine delivery temperature for two ambient ranges temperatures between 3 and 211uC at constant brine flow rate of 0?64 kg s 21. The unit was installed in open air and hence it was not possible to control the ambient conditions. However, during the tests the variation of the ambient conditions was not very wide and hence the results have been grouped into two sets, one for 16?5 1?5uC and the other for 20 1?5uC. The test results provided data for the inlet and outlet temperatures of each component of the absorption system (such as the evaporator, solution cooled absorber, air cooled absorber, pump, generator, levelling chamber, rectifier, condenser, heat exchangers and expansion device) as well as the pressures in the high and low pressure sides of the system. The temperature results revealed an average temperature for the vapour ammonia leaving the generator of approximately 100uC. The evaporator outlet temperatures varied between 216 and 23uC for the range studied, while the condenser outlet temperature was approximately 28uC. The low side pressure varied between 1?06 and 2?1 bar (gauge) while the high side pressure ranged between 11?0 and 13?8 bar (gauge). The obtained temperatures and gas consumption values were used to calculate the refrigeration outputs and the coefficient of performance (COP) of the unit at different brine delivery temperatures and ambient conditions. The COP was calculated as the ratio of cooling performed by the evaporator to the thermal energy input to the system (this energy was determined by multiplying the gas consumption by its calorific value). The results are shown in Fig. 5. Analyses of the 6 Basic schematic diagram of typical CHRP food chilling plant 188 Journal of the Energy Institute 2008 VOL 81 NO 4

5 experimental results revealed that both the refrigeration output and the COP of the unit decreased with decreasing brine delivery temperature. The obtained refrigeration capacity varied between 8?5 and 15 kw c and the COP between 0?32 and 0?57, for brine delivery temperatures between 211 and 3uC. Application in chilled food processing The food industry is a diverse industry so any example selected is not necessarily a generic application, which could address every reader s preference, so a typical application where a CHRP system could be applied is considered. Assuming a chilled food application where a liquid food product is to be pasteurised and cooled to a chill temperature using a spiral chiller 17 asshowninfig.6.the details highlighted below will be taken as an application for a CHRP comparison with conventional utility supply. Based on chilled dairy product, where the raw material is held at chill temperature, then processed, pasteurised, cooled, packaged into pots at 30uC through plate heat exchangers 18 and then cooled as quickly as possible in the package by subjecting the product to a horizontal air flow at 25uC in a spiral tunnel (with brine flowing at 28uC from absorption chillers). Capacity of the chilled plant is assumed of 1000 kg h 21. The product is pasteurised from 5 to 76uC and processed then cooled down to 30uC, where it is filled into pots and then chilled in a single drum spiral chiller to 3uC, ready for cartooning and shipping to the distribution system. 16 A relative comparison between conventional and CHRP system has been analysed using data with some typical commercial costs as shown in Tables 1 and 2. Energy outputs from a typical CHRP food chilling plant is presented in Table 3. The results of economical, Table 1 Data for system comparisons* Conventional system Electrical demand Multirack compressors, kw e Fans, lighting, auxiliary equipment for VCR, kw e 25 Average grid mix electrical efficiency, % 38 Heat demand Process heating, kw th 36 Gas fired boiler Fuel Natural gas Thermal efficiency, % 80 Electric driven VCR COP el 2. 0 Installed cost, /kw c 160 OM cost, /(kw c year) 70 CHRP system Microgas turbine Number of units 1 Electrical power output/unit, kw e 80 Thermal output, kw th 155 Electrical efficiency, % 28 Exhaust gas temperature, uc 278 Installed cost, /kw e 982 OM cost, /kwh Absorption chiller Number of units 5 Cooling capacity/unit, kw c 12 COP at brine delivery temperature of 28uC 0. 5 Installed cost, /kw c 569 OM cost, /(kw c year) 40 *OM: operation and maintenance; VCR: vapour compression refrigeration. energy and environmental comparisons of the conventional plant and CHRP system are presented in Table 4, which based on a 6500 h production per annum. AscouldbeseeninTable4,thesimplepaybackonthe extra investment is less than four years. This is expected to reduce to less than three years by using absorption units with COP s closer to one. The primary energy savings for the typical chilled food processing plant yields around 27% and the annual CO 2 emission savings obtained is 33% or approximately 76 t. Clearly, as the scale of the project is widened and a system is embedded into a new factory, then the relative advantage can be more pronounced expecting to reduce the capital cost, primary energy consumption and CO 2 emissions. Figure 7 shows the influence of the gap between electricity and gas prices (otherwise known as the spark gap) on the payback period. From the figure, it can be seen that in the event the spark gap closes from 7?2 to 3?4/ kwh, then the payback increases rapidly from 2?8 to 17?3 years. For the case studied, the spark gap of 6?05/kWh provides 3?7 years in the payback period. It is difficult to imagine this gap will close in the UK where there is such a dependency on gas to generate electrical energy and its future dependency looks sure to be maintained. Conclusions The feasibility analysis of the application of CHRP system in a chilled dairy product plant based on the results obtained from experimental works has shown the following. 1. The CHRP technology can provide promising savings in perspective of energy, economic and environment. The case studied revealed a primary energy saving of 27%, payback time of 3?7 years and annual CO 2 emission reduction of 33% based on utilisation of one unit of MGT and five units of absorption chillers. Table 2 Utility prices and CO 2 emission factors* Energy prices (excluding CCL and VAT) 19 Natural gas, p/kwh { Electricity purchased from National grid, p/kwh { Electricity exported, p/kwh CCL rates 20 Electricity, p/kwh Natural gas, p/kwh VAT, % CO 2 emission factors 21 Grid electricity, kg/kwh Natural gas, kg/kwh *CCL: climate change levy; VAT: value added tax. { Firm contract (uninterruptible supply) average prices of three quarters in { Small size user with annual consumption,880 MWh average prices of three quarters in Assuming 50% of the electricity purchased price. Table 3 Energy output Energy output from typical CHRP plant* MGT electrical power output, kw e 80 PHX 1 regenerative process heat transfer, kw th 29 PHX 2 resultant process heating, kw th 36 Absorption chiller spiral freezer 55 resultant process cooling, kw c *PHX: plate heat exchanger. Journal of the Energy Institute 2008 VOL 81 NO 4 189

6 Table 4 Economic and environmental comparisons of conventional and CHRP systems for chilled food processing Indicators Conventional plant CHRP plant Capital cost, (refrigeration plantzheating) (based on MGT) Electrical requirement, kw e (to drive the fans, lights etc.) Exported electricity, kw e 0 55 Gas consumption, kw f Annual running cost, Annual equivalent exported energy cost Annual OM cost, Annual net running cost, Annual primary energy consumption, kwh Capital cost difference, z Net running cost difference, Payback on the difference, years 3. 7 Annual primary energy savings, % 27 Annual CO 2 emission savings, t 76 Annual CO 2 emission reduction, % With the current installed costs of MGT based CHRP systems their economic viability is very sensitive to the price gap between natural gas and grid electricity. This spark gap prices should be greater than 6?05/kWh to obtain reasonable payback time of less than four years. 3. The environmental benefits of the CHRP over conventional systems are to a large extent dependent on the COP of the absorption refrigeration system. For the low temperature cooling application considered, the COP of the absorption system should be greater than 0?5. This is expected to be achievable in large scale applications 4. The cost of MGT based CHP systems is currently approximately double the cost of engine based CHP units. It is expected that the initial commercial applications may be designed around reciprocating engines in order to provide a reasonable incentive with respect to the incremental payback. With increasing number of applications and further development, the cost of MGT is expected to decrease and this should increase their economic attractiveness. 5. In terms of the wider use in the food industry at present there are no low temperature absorption refrigeration systems available off-the-shelf and this contributes to their high capital cost. Mass production of exhaust gas drivensystemsisexpectedtoreducetheinstalledcostof CHRP systems and increase their range of applications. Acknowledgements The authors wish to acknowledge the Food Technology Unit of DEFRA for their financial support for this 7 Influence of spark gap prices on payback period project and the contribution of the industrial collaborators, Bond Retail Services Ltd, Apex Air Conditioning and Bowman Power. The first author greatly acknowledges PhD programme studentship provided by the TPSDP Project of Refrigeration and Air Conditioning Study Programme (RASP), Bali State Polytechnic, Indonesia and the School of Engineering and Design, Brunel University, UK. References 1. Available at: index.htm (accessed on 15 December 2006). 2. Environmental impacts of food production and consumption: final report to DEFRA, Manchester Business School, Manchester, UK, December N. Sugiartha, I. Chaer, S. A. Tassou and D. Marriott: Proc. 5th Int. Conf. on Fluid and thermal energy conversion, Jakarta, Indonesia, December 2006, Institut Teknologi Bandung, Paper Our energy future-creating a low carbon economy, Energy White Paper, Department of Trade and Industry, London, UK, The energy challenge energy review report, Department of Trade and Industry, London, UK, Digest of United Kingdom energy statistics, TSO, Crown, UK, S. A. Tassou, I. Chaer, N. Sugiartha and D. Marriott: Proc. 19th Int. Conf. on Efficiency, cost, optimization, simulation and environmental impact of energy systems, Crete, Greece, July 2006, National Technical University of Athens, Volume 3, S. A. Tassou: Heat Recov. Syst. CHP, 1989, 9, S.A. Tassou, P.P. Votsis, and C. Keravnou: Heat Recov. Syst. CHP, 1994, 14, P. A. Pilavachi: Appl. Therm. Eng., 2002, 22, J. C. Ho, K. J. ChuaandS. K. Chou: Renew. Energy, 2004, 29, P. A. Katsigiannis and D. P. Papadopoulos: Energ. Convers. Manag., 2005, 46, A. A. Jalalzadeh-Azar, S. J. Slayzak and J. P. Ryan: ASHRAE Trans., 2002, 108, Available at: (accessed on 18 February 2006). 15. Available at: (accessed on 10 January 2006). 16. Available at: (accessed on 20 September 2007). 17. Available at: (accessed on 18 September 2007) 18. Available at: (accessed on 20 September 2007). 19. Quarterly energy prices December 2007, BERR, London, UK, Climate Change Levy (CCL)-rates to rise at 1 April 2007, (accessed on 10 December 2007). 21. Guidelines to DEFRA s GHG conversion factors for company reporting, available at: business/envrp/conversion-factors.htm (accessed on 20 December 2007). 190 Journal of the Energy Institute 2008 VOL 81 NO 4

Sorption Refrigeration Systems & their Application to the Food Industry

Sorption Refrigeration Systems & their Application to the Food Industry Articles about Doug Marriott Associates Doug Marriott A PRESENTATION MADE AT BRUNEL UNIVERSITY IN THE UK AND 14 INDUSTRIAL PARTNERS