energy savings in primary food cooling - grimsby institute · energy savings in primary food...
TRANSCRIPT
Mark SwainFood Refrigeration & Process Engineering Research Centre, University of Bristol
Energy savings in primary food cooling
National Motorcycle Museum3rd April 2009
Introduction - primary cooling
• Meat – primary carcass chilling• Dairy – milk cooling on the farm• Potatoes – bulk cooling and storage• Blast freezing – potato products
Energy – where used?
• Compressor – electric motor drive• Evaporator fans• Condenser fans• Defrost heaters – heating elements• Lighting• Pumps• Auxiliary fans
Energy saving – refrigeration
Only 3 ways to cut refrigeration energy use:
• Minimize heat load
• Minimize auxiliary electrical consumption
• Increase efficiency of refrigeration equip.
Energy saving – heat load
Made up of:• Product load – heat from food• Infiltration load – air leaks/open doors• Transmission load – through fabric• Heat from other sources in room –
• fan/pump motors• defrost heaters• racking/trolleys• people
Energy use in meat chilling
• Refrigeration accounts for 45 - 90% of electrical consumption in abattoirs
• Up to 80% is for primary carcass chilling
Energy use in meat chilling
• Beef primary chilling UK• Minimum 19 kWh/tonne• Average 32 kWh/tonne• Maximum 52 kWh/tonne
• Pork primary chilling UK• Minimum 25 kWh/tonne• Average 43 kWh/tonne• Maximum 72 kWh/tonne
Note - Large range
Energy saving – heat load
Made up of:• Product load – heat from carcass
Little can be done unless process changed? • Infiltration load – air leaks/open doors
Door discipline/air curtains?• Transmission load – through fabric
Set by design specification?• Heat from other sources in room
Evaporator fans and defrost optimisation?
Air infiltration - solutions
• Door maintenance - mechanisms, seals• Strip curtains (up to 90% effective)• Improved door discipline• Door monitoring and alarms• Automatic/rapid doors• Vestibules/air lock• Air curtains (up to 80%)• Shut doors – 100% effective
Infiltration – air curtain
Thermoscreens Ltd
Up to 80% as effective as door
Heat load from other sources
Evaporator fans:• Electric motors (counts x2)• Fan power increases with cube of velocity• Fan speed controllers – reduce speed• High efficiency fan motors/fan bladesDefrost heaters:• Minimize defrost cycles (counts x2)• Defrost on demand
Energy saving – refrigeration equipment
Increase efficiency of compressor etc:
Coefficient of Performance
COP = Refrigeration effect (kW) .
Power input to compressor (kW)
Condenser
Evaporator
Expansion valve Compressor
Refrigeration circuit components
Energy saving - evaporator
• Increase evaporating temperature(1°C = 1 to 4% saving)
• Large heat transfer surfaces• Efficient fan motors and control• Keep clean
Energy saving - condenser
• Decrease condensing temperature(1°C = 1 to 4% saving)
• Large heat transfer surfaces• Efficient fan motors and control• Keep clean
Variable load profile – meat chilling
0
1
2
3
4
5
6
7
8
9
26-Feb 27-Feb 28-Feb 01-Mar 02-Mar 03-Mar 04-Mar 05-Mar
Energy saving - compressor
• Match capacity – peak load / average load• Compressors less efficient at part load• Variable speed drives• Multi-compressor pack
Milk cooling – raw milk on farm
• Leaves udder at approx 37°C• Cooled to below 4°C on farm• Penalty for higher temperature• Collected by tanker daily or every other
day
Milk cooling – ice bank cooler
• Stirred bulk storage tank• Chilled water spray• Ice builds on coil• Remote refrigeration unit
Source: DeLaval
Milk cooling – DX system
Source: DeLaval
• Stirred bulk storage tank• Integral evaporator• More efficient than ice bank• Remote refrigeration unit
Milk cooling – pre-cooling
Source: DeLaval
• Stirred bulk storage tank• Plate heat exchanger• Ice builder• Mains / well water + chilled• Remote refrigeration unit
FEC Services
Milk cooling – energy saving
• Ice bank – least efficient• DX system – better• Pre-cooling + DX system – best
• Use scroll compressor – 15 to 20% more efficient than reciprocating compressors
Potato cooling/storage - bulk raw
• Main issues:• Old stores - insulation and air infiltration
FEC Services
Potato cooling/storage - bulk raw
• New case study by Potato Council Ltd• Store X purpose-built potato store
53.2 kWh/tonne• Store Y converted grain store
116.3 kWh/tonne – closed & modified
Store X Store Y
Potato cooling/storage - bulk raw
• Main issues:Newer stores – compressor/evaporator fans
Potato cooling/storage - bulk raw
FEC Services
Blast freezing - potato products
• Potato products emerge from fryer at 80°C
• Need to be frozen to -12°C before packaging
• Process rate 4.5 tonnes/h• Spiral freezer incapable of
extracting initial heat load • Initial moisture loss
freezes on coils
Blast freezing - ambient cooling
0
20
40
60
80
100
Start 5 minutes 10 minutes
Tem
pera
ture
(°C
)
0
50
100
150
200
5 minutes 10 minutes
Ener
gy lo
ss (k
J/kg
)
SensibleEvaporativeTotal
31% 44%of heat load
20°C, 1 m/s
Blast freezing - ambient cooling
• 5 minutes of ambient cooling• Removes 562,500 kJ of heat energy
from 4.5 tonnes of product per hour• Stops 60 kg/h of water freezing on coils• Insignificant increase in freezing time• Increases energy efficiency of process
Energy saving measures - summary
• Reduce infiltration• Ensure good insulation• Increase evaporating temperatures• Reduce condensing temperatures• Keep defrost cycles to a minimum• Reduce fan speeds once heat removed• Use high efficiency electric drives• Proper maintenance schedules• Monitor and target energy consumption
SPECIFY & DESIGN PROCESS/SYSTEM CORRECTLY