Low-Grade Heat Recovery in
UK Food/Drink Industry
Richard Law
Speaker Background
• 2nd 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)
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
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…
Waste Heat Recovery
Meeting carbon budgets - 3rd Progress Report to Parliament (2011). Department of Energy and Climate Change
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!
Waste Heat Recovery
• Why?
– Rising Cost of Key Utilities:
Department of Energy and Climate Change
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)
Total
F&D sector
Cost per
unit gas
(£/kWh)
Greenhouse
gas emissions
per unit
(kg/kWh)
Potential
cost savings
per year
(£m/year)
Potential
emissions
savings per year
(tCO2eq/year)
11.4 x 109
0.0321
0.1836
£365.94m
2,093,040
2.8 x 109
0.0321
0.1836
£89.88m
514,080
Waste Heat Recovery
• Big incentive for waste heat recovery in the
sector
– Potential cost savings of around £90m
– Potential CO2 savings of over 500,000 tonnes
…Waste heat recovery should not be ignored!
Scope of Study
• Low-grade waste heat recovery:
– Streams of less than ≈260oC
– 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…
Sector Energy Use
• Sector consumes around 42TWh of energy
each year
– Around 25% of the total for all processing
industries
Sector Energy Use
Other uses
15%
Refrigeration
7%
Electric motors
7%
Drying/separation
7%
Low temperature
(<300deg.C) processes
64%
Drying/separation:
Electric
‘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,
spacespray
heating,
dryers
andetc
•Includes common processes such
•Also
instrumentation.
mostly occurs at lowas baking, frying, pasteurisation etc
temperature
Unlikely to include
(< ~200°C)
a significant
amount of high temperature
(>300°C) processes
Sector Energy Use
• At least 85% of the sector energy use is
consumed at temperatures of less than 300oC
• Fair assumption that most (if not all) of the
waste heat available will be in the low-grade
range
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 60oC hot
water, or 40oC air heat source
– Boiler: Flue is commonly vented at around 200oC
despite the availability of economisers etc
– Spent cooling water, condensate return: up to
150oC (pressure dependant)
Sources of Low-Grade Heat
• Sector-Specific operations:
– Cooking of food: Fryers or Ovens
• Gas/Vapour heat source at 150-200oC
– Drying of food products: Spray or rotary dryers etc
• Air/Vapour heat source from exhaust at 90-160oC
– Evaporation & Distillation processes:
• Typically produce water vapour heat source at ~100oC
– Refrigeration:
• Water heat source at condenser at around 60oC
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)
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
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)
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
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
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 100oC)
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…
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?
Heat Recovery Technology
Danish Technological Institute case study: Industrial cleaner
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
Heat Recovery Technology
Organic Rankine Cycle
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
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
Heat Recovery Technology
Organic Rankine Cycle
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
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
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
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
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 tCO2eq/year
• Various options for waste heat recovery: Heat
exchangers, Heat Pumps etc
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
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