Opportunities for Low-Grade Heat Recovery in the UK Food Processing Industry

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David Reay Sustainable Thermal Energy Management in

1 Opportunities for Low-Grade Heat Recovery in the UK Food Processing Industry Richard Law*, Adam Harvey, David Reay Sustainable Thermal Energy Management in the Process Industries International Conference (SusTEM2011)

2 Author Background 1 st year PhD Student at School of Chemical Engineering and Advanced Materials, Newcastle University Working on EPSRC funded OPTITHERM project: OPTImising THermal Energy Recovery, utilisation and Management Overall aim to produce an Expert System for the selection of best available technology for the recovery of low-grade industrial waste heat Part of Process Intensification Group (PIG) See for information

3 Introduction: Why recover waste heat? Climate Change Act (2008) Targets 80% reduction in greenhouse gas emissions by 2050, 34% by 2020 Won t achieve the targets (based on current trends) Carbon Taxes to be introduced in 2013

4 Introduction: Why recover waste heat? Meeting carbon budgets - 3rd Progress Report to Parliament (2011). Department of Energy and Climate Change

5 Introduction: Why recover waste heat? Processing Industries account for 20-25% of greenhouse gas emissions Demand for industrial produce unlikely to drop Especially in food/drinks processing: people need to eat! Reduce energy consumption (and emissions) by increasing overall plant efficiency By recovering waste heat

6 Introduction: Why recover waste heat? Economic incentive: Fuel prices for manufacturing industry, in cash terms from Quarterly Energy Prices (2010). Department of Energy and Climate Change

7 Introduction: Available Waste Heat It is estimated that 11.4TWh of recoverable waste heat is emitted to environment per year via waste streams in process industries Around 5% of total energy use 2.8TWh from food/drinks processing 5-7% of total energy use Enough energy to heat ~160,000 homes Recovery of this heat would be significant in reducing emissions and costs

8 Scope of study Low-grade waste heat recovery: Streams of < ~260 C* Food Industry: All food/beverages processing: e.g. meat and fish production, dairy, brewing, bakery etc Including production of animal food Chosen because most processes occur at low temperature. Therefore, many low-grade heat sources * Profiting from low-grade heat. (1994) Watt Committee

9 Energy use in the sector Electric motors and refrigeration systems also emit low-grade heat Refrigeration 7% Electric motors 7% Other uses 15% Other uses includes generic energy consumers such as lighting, space heating, and instrumentation. Unlikely to include a significant amount of high temperature (>300 C) processes Low temperature (<300deg.C) processes 64% Drying/separation 7% Drying/separation: Includes distillation, evaporation tanks, spray dryers etc Also mostly occurs at lowtemperature (< ~200 C) Low-temperature processes: Dominates energy use Includes common processes such as baking, frying, pasteurisation etc

10 Energy use in the sector Consumes around 42TWh of energy each year Around 25% of total for process industries At least 85% of the sector energy use is consumed at temperatures of less than 300 C Fair assumption that the vast majority (if not all) of waste heat will be available in the low-grade range

11 Sources of low-grade heat Sources of low-grade heat from both generic and sectorspecific processes Generic unit operations include: Air compressors: Cooled to produce 60 C Water heat source or 40 C Air heat source Boiler: Flue is commonly vented at ~200 C despite availability of economisers and air pre-heaters Spent cooling water, condensate return: upto 100 C

12 Sources of low-grade heat Sector specific operations: Cooking of food: Fryers or ovens etc Gas/Vapour heat source at C Drying food products: Spray or rotary dryers etc Air/vapour heat source from exhaust at C Evaporation & Distillation processes Typically produce water vapour heat source at ~100 C Refrigeration Water heat source at around 60 C

13 Potential uses of waste heat Heat transfer between source and sink Simplest solution Sector-specific or generic heat sinks (linked to energy usage) Often a surplus of waste heat (esp. low-grade) Other options should be explored: Upgrade waste heat: Via heat pump (open or closed cycle) Convert waste heat: To electricity: ORC or thermoelectric unit To refrigeration via absorption chillers

14 Heat recovery technology For heat transfer between source and sink: Direct re-use Simple solution: requires only pipe work and auxiliary equipment Not always suitable in food industry: contamination problems Heat Exchangers Many available, each has own merits Full details of each type found in paper

Heat recovery technology The Rotating Regenerator (Heat Wheel): Generic advantages: Gas-Gas applications High effectiveness (>90%) Off-the-shelf purchase (lower cost) Food-industry specific

15 Heat recovery technology The Rotating Regenerator (Heat Wheel): Generic advantages: Gas-Gas applications High effectiveness (>90%) Off-the-shelf purchase (lower cost) Food-industry specific advantages: Can be designed to facilitate self cleaning (fouled streams, e.g. dryer exhaust) Can recover latent heat (e.g. dryer exhaust, over/fryer exhaust) Has been demonstrated in heat recovery of dryer exhausts, to heat fresh air for space heating (CADDET, 1998) Image from

16 Heat recovery technology The (liquid-liquid) Plate Heat Exchanger: Can be used for almost all heat exchanger duties (exc. extreme pressure and temperature - unlikely in WHR) May be joined by gaskets, brazed or welded depending on operating conditions Constructed from a wide range of materials Gasketted plate heat exchanger allows ease of access for cleaning (useful for fouled streams found in food industry) Low approach temperature Compact size eases retro-fit burden Image from

17 Heat recovery technology (Closed-Cycle) Vapour Compression Heat Pump: Surplus of waste heat expected in many food processing plants due to many heat sources of < 100 C. May not be a matching heat sink Heat Pump may provide solution Temperature lifts in excess of 50 C recently reported for COP of greater than 3 Heat pumps with condenser temperature greater than 150 C in development

18 Heat recovery technology (Closed-Cycle) Vapour Compression Heat Pump: Attitude towards heat pumps poor in UK food industry: 36% engineers (Sinclair, 2001) consider heat pumps risky or are unsure Evidence of heat pump utilisation should be presented to UK food industry engineers to help change opinion Modular, off-the-shelf, heat pump solutions may also help increase confidence For example, from recent Heat Pump summit

19 Heat recovery technology Danish Technological Institute case study: Industrial cleaner

20 Heat recovery technology Danish Technological Institute case study: Industrial cleaner Heat source: Humid air leaving the cleaner Heat sink: Hot water input to the system COP: 4 Small scale: 25kW output per unit Energy consumption to unit cut by 50% Payback time: 1.5 to 3 years (only four month into demonstration) Saving 49 tonnes of CO2 per unit, per year Risky? Unsure?

21 Heat recovery technology Danish Technological Institute case study: Industrial cleaner

22 Heat recovery technology (Open Cycle) Mechanical Vapour Recompression:

23 Heat recovery technology (Open Cycle) Mechanical Vapour Recompression: MVR used to compress vapour leaving an evaporative process, which may then be used to heat the evaporator contents Food/beverages industry runs a lot of evaporation and distillation processes (concentration of fruit juices, brewing, distilleries etc) COP in the region of 10 are commonly reported. This may lead to small pay-back periods Common in whiskey distilleries in Scotland. Large potential for expansion into other food/industry subsectors - brewing, soft drinks etc

24 Heat recovery technology Organic Rankine Cycle:

25 Heat recovery technology Organic Rankine Cycle: ORC recovers low-grade heat to generate electricity Waste heat source temperature as low as 85 C (in current operation in Europe) or 40 C (research stage) Useful when surplus of low-grade waste heat is present: all plants require electricity! Technology has yet to seriously take-off in UK Problems: Low efficiency - only 5-18% efficient (electricity produced/heat recovered) Demonstration schemes and modular units required to spark interest in this technology

26 Heat recovery technology Organic Rankine Cycle: DRD Power currently demonstrating a 200kW unit at a chemical site on Teesside Modular, skid-mounted unit - minimal retrofit (providing there is space): just pipe-in the heat source, wire-in the generator ~100 C vapour heat source Demonstration scheme published by Carbon Trust Expected payback time quoted as ~3years More demonstration schemes and/or modular units will lead to increasing interest in ORC for waste heat recovery in UK

27 Heat recovery technology Organic Rankine Cycle:

28 Selection of WHR technology Select method of WHR according to the simplest appropriate solution, and ultimately the payback time Simplest, cheapest solution is direct re-use of the heat source into the heat sink Requires only pipe/duct work Next level: Heat transfer via heat exchanger More expensive than direct re-use More equipment (heat exchanger) required and larger installation cost

Selection of WHR technology Next level: Heat Pump/ORC Solution When a surplus of waste heat is present Requires combination of heat exchangers, compressors/pumps etc Complex,

29 Selection of WHR technology Next level: Heat Pump/ORC Solution When a surplus of waste heat is present Requires combination of heat exchangers, compressors/pumps etc Complex, high capital cost solution Final option: Secondary Enterprise/Over the Fence heat sink Requires significant research Large capital to set up project Not often considered in UK

30 Conclusions 2.8 TWh of recoverable waste heat is emitted to environment from the food processing industry per annum of which at least 85% is of low-grade Various options for WHR: heat exchangers, heat pumps, ORC etc WHR technology should be chosen according to the simplest appropriate solution (and project economics) Often a surplus of low-grade heat present: potential for heat pumps and ORC Demonstration schemes should be set-up to encourage the uptake of ORC and HP projects (including MVR) Development of further modular ORC and HP solutions would also encourage uptake of such projects

31 Acknowledgements Supervisors: Dr Adam Harvey - PIG group, School of Chemical Engineering and Advanced Materials, Newcastle University Prof. David Reay David Reay and Associates (Visiting Prof. at Newcastle University) EPSRC (Project no. EP/G061467/1) Collaborating partners on OPTITHERM project: Brunel University Northumbria University A number of industrial partners

32 Thanks for listening, Any Questions?

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