Low-Grade Heat Recovery in UK Food/Drink Industry. Richard Law

Transcription

1 Low-Grade Heat Recovery in UK Food/Drink Industry Richard Law

2 Speaker Background 2 nd year PhD student at the School of Chemical Engineering and Advanced Materials Working on design of novel waste heat recovery systems Heat Pumps, organic Rankine cycles and heat exchangers Developing software for the selection of the best available technology for waste heat recovery (on an individual heat source basis)

3 Highlights Introduction to waste heat recovery inc. the economic and environmental benefits Energy use in the sector Typical waste heat sources Potential uses of waste heat Waste heat recovery technology

4 Waste Heat Recovery Why? Climate Change Act (2008) Targets an 80% reduction in greenhouse gas emissions by 2050 (34% by 2020; based on 1990 levels) Based on current trends, we will NOT achieve these targets

5 Waste Heat Recovery Meeting carbon budgets - 3rd Progress Report to Parliament (2011). Department of Energy and Climate Change

6 Waste Heat Recovery Why? Processing industries account for 20-25% of greenhouse gas emissions Around a quarter of which from Food/drink sector Demand for industrial produce is unlikely drop (especially in food/drinks processing) Reduce industrial energy consumption (and greenhouse gas emissions) by increasing energy efficiency by recovering waste heat!

7 Waste Heat Recovery Why? Rising Cost of Key Utilities: Department of Energy and Climate Change

8 Waste Heat Recovery 11.4TWh of recoverable waste heat emitted to environment each year via waste streams (5% of energy use) 2.8TWh from food industry (~7% of energy use) Units of waste energy per year (kwh/year) Cost per unit gas ( /kwh) Greenhouse gas emissions per unit (kg/kwh) Potential cost savings per year ( m/year) Potential emissions savings per year (tco 2 eq/year) Total 11.4 x m 2,093,040 F&D sector 2.8 x m 514,080

9 Waste Heat Recovery Big incentive for waste heat recovery in the sector Potential cost savings of around 90m Potential CO 2 savings of over 500,000 tonnes Waste heat recovery should not be ignored!

10 Scope of Study Low-grade waste heat recovery: Streams of less than 260 o C Often the most difficult to recover Food industry: All food/beverage processing: dairies, breweries, bakeries, industrial fryers etc (inc. animal food) Chosen as most processes occur at low temperatures, therefore many low-grade heat sources

11 Sector Energy Use Sector consumes around 42TWh of energy each year Around 25% of the total for all processing industries

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

13 Sector Energy Use At least 85% of the sector energy use is consumed at temperatures of less than 300 o C Fair assumption that most (if not all) of the waste heat available will be in the low-grade range

14 Sources of Low-Grade Heat Heat sources can be from both generic and sector-specific processes Generic unit operations include: Air compressors: Cooled to produce 60 o C hot water, or 40 o C air heat source Boiler: Flue is commonly vented at around 200 o C despite the availability of economisers etc Spent cooling water, condensate return: up to 150 o C (pressure dependant)

15 Sources of Low-Grade Heat Sector-Specific operations: Cooking of food: Fryers or Ovens Gas/Vapour heat source at o C Drying of food products: Spray or rotary dryers etc Air/Vapour heat source from exhaust at o C Evaporation & Distillation processes: Typically produce water vapour heat source at ~100 o C Refrigeration: Water heat source at condenser at around 60 o C

16 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 (using heat pump) Convert waste heat: To electricity (using ORC etc) To refrigeration (using absorption chiller)

17 Heat Recovery Technology For heat transfer between source and sink: Direct re-use Very simple solution Not always suitable in food industry (contamination issues) Heat Exchangers: Many available, tailored for various types of fluids Can provide a very economical solution

18 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)

19 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

20 Heat Recovery Technology Other Heat Exchangers: Shell and Tube: Very well known technology Wide-range of materials, inc. glass: useful for heavily fouled or greasy streams Scraped-Surface: For heat transfer involving complex rheologies Run-Around Coil: When cross-contamination cannot be tolerated

21 Heat Recovery Technology (Closed-Cycle) Heat Pumps 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 (current technology limited to 100 o C)

22 Heat Recovery Technology (Closed-Cycle) Heat Pumps 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

23 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?

24 Heat Recovery Technology Danish Technological Institute case study: Industrial cleaner

25 Heat Recovery Technology Mechanical Vapour Recompression (MVR) 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 leads to small pay-back periods (as low as 2 years) Common in whiskey distilleries in Scotland. Large potential for expansion into other food/industry subsectors - brewing, soft drinks etc

26 Heat Recovery Technology Organic Rankine Cycle

27 Heat Recovery Technology Mechanical Vapour Recompression (MVR) 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 leads to small pay-back periods (as low as 2 years) Common in whiskey distilleries in Scotland. Large potential for expansion into other food/industry subsectors - brewing, soft drinks etc

28 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

29 Heat Recovery Technology Organic Rankine Cycle

30 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

31 Selection of WHR technology Select method of WHR according to the simplest appropriate solution, and ultimately the payback time Next level: Heat transfer via heat exchanger More expensive than direct re-use More equipment (heat exchanger) required and larger installation cost

32 Selection of WHR technology Select method of WHR according to the simplest appropriate solution, and ultimately the payback time 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

33 Selection of WHR technology Select method of WHR according to the simplest appropriate solution, and ultimately the payback time Final option: Secondary Enterprise/Over the Fence heat sink Requires significant research Large capital to set up project Not often considered in UK

34 Conclusions 2.8TWh of recoverable waste heat is emitted to the environment each year from the food/drinks sector Full recovery has the potential to save around 90m/year and 500,000 tco 2 eq/year Various options for waste heat recovery: Heat exchangers, Heat Pumps etc

35 Interest? My supervisor, Prof. David Reay, and I have experience in feasibility and design studies for many types of waste heat recovery systems Including heat recovery by heat exchanger, and heat pump Technical, economic and environmental assessment We may be available to carry out such work in the coming months For enquiries: richard.law1@ncl.ac.uk or dareay@aol.com

36 Thank You I d like to thank: My PhD supervisors: Prof. Harvey and Prof. Reay Dr Barbara Sturm (for inviting me to talk) Everyone for listening