Download Opportunities for low-grade heat recovery in the UK food processing

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)
Author Background
 1st 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 http://pig.ncl.ac.uk for information
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
Introduction: Why recover waste heat?
Meeting carbon budgets - 3rd Progress Report to Parliament (2011). Department of Energy and Climate Change
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
Introduction: Why recover waste heat?
 Economic incentive:
“Fuel prices for manufacturing industry, in cash terms 1990-2009” from Quarterly Energy Prices (2010).
Department of Energy and Climate Change
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
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
Energy use in the sector
Electric motors and refrigeration
systems also emit low-grade heat
Other uses
15%
Refrigeration
7%
Electric motors
7%
‘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
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
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
Sources of low-grade heat
 Sector specific operations:
 Cooking of food: Fryers or ovens etc
 Gas/Vapour heat source at 150-200°C
 Drying food products: Spray or rotary dryers etc
 Air/vapour heat source from exhaust at 110-160°C
 Evaporation & Distillation processes
 Typically produce water vapour heat source at ~100°C
 Refrigeration
 Water heat source at around 60°C
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
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 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 www.datacentreknowledge.com
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 www.alfalaval.com
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
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…
Heat recovery technology
Danish Technological Institute case study: Industrial cleaner
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
(Open Cycle) Mechanical Vapour Recompression:
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
Heat recovery technology
Organic Rankine Cycle:
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…
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
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, 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
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
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
Thanks for listening,
Any Questions?