Phil Scott, AMEC

1. DEVELOPING BIORESOURCES
THROUGH AD
#UKADBiogas @adbioresources
CHAIR:
DR ADRIAN HIGSON, NNFCC
PANEL:
PROF CHRISTOPHER RAYNER, C-CAPTURE
STEVE BROOME, CPI
PHIL SCOTT, AMEC
JOHN WILLIAMS, ADAS UK
DR DONNA RAWLINSON, NORTHUMBRIA WATER

3. 01 July 2015
Digestion and Greenhouses
Synergistic Resource Recovery
Phil Scott:
Technical Director
Amec Foster Wheeler

4. Objectives for Today
1. To show where AD by-products have value to growers
2. To explain what greenhouse operators want
3. To demonstrate the potential value.
4

5. Burning Digester Gas
CH4 + 2O2 => 2H2O + CO2 + Heat
Mostly
(60 to 90%)
wasted
All
wasted
All
wasted
So, who needs these wasted products?

6. Horticulturalists

7. Supply and Demand
AD plant by-products = Greenhouse requirements

8. AD Resource Sources
Heat sources;
► Wasted CHP hot water
► CHP exhaust gas
► Gas boiler flue gas
► Various coolers (e.g. pasteurisation plant)
► Digested sludge
► Bio-gas chilling plant
► Boiler blow-down
Carbon dioxide sources;
► CHP exhaust gas
► Steam boiler flue gas
► Digester gas
Nutrient sources;
► Digestate
Available AD
resources are
dependent
upon the design
of the AD plant

9. Characteristics of Viable Resources at a Typical AD Plant
CHP Hot Water
► 85oC
► Easily accessible
CHP/Boiler Exhaust Gas
► CO2 rich because burning digester gas
► Oxides of trace components in digester gas
► Oxides of nitrogen
► Requires treatment
Digestate
► May be microbiologically clean
► Rich in nitrogen and phosphorous

10. Greenhouses – Background Information
Greenhouses referred to by their plan area
► 2.5Ha is a typical size of greenhouse
► Largest in UK is 23Ha (as of 2012)
► Most are in the east of the UK
Tomatoes in the UK
► Industry in the UK supplies only 15% of consumer demand
► Worth £175,000,000 per year
► From 200Ha of greenhouse
► Approximately 5 main growers
► Fiercely competitive
► Looking for an edge, but not open to risk

11. Greenhouse Demands
Heat
Heat Using rule of thumb
► Rule of thumb used by the industry is 450kWh/m2
► Clearly this varies with the growing season
► Runs from February to November, until there is insufficient sunlight
► Further heating then becomes pointless
Calculated by engineers
► Based on:
► losses (structural, air changes and evaporation), and;
► gains from insolation
► Accurately predicts when heat is required
► Guaranteed heat requires zero to 900kWh/m2 depending on the season

12. Greenhouse Demands
Carbon Dioxide
► Factors to consider:
► On a very sunny day in northern England, tomatoes’ maximum uptake rate is saturated above
1000ppm (normally a lot less)
► Normal atmospheric CO2 is 350 to 400ppm
► OSHA recommended limit for occupational exposure is 1000ppm
► Nearest UK HSE equivalent is 5000ppm for 8 hours
► Hence, target demand figure is 1000ppm of CO2 in the greenhouse
► This typically means that 35% to 80% of CHP exhaust gas is not needed

13. Delivery of Heat and CO2 to Greenhouse
Hot water relatively simple
► Pumps and pipes
► Hot well (to provide buffer capacity)
Carbon Dioxide delivery is trickier
► Needs to be cleaned
► Needs to be cooled
► Needs to be conveyed cost-effectively

14. Cleaning the CHP Exhaust Gas
Standard approach is a catalytic converter plus urea injection
► The ‘cat’ removes the trace oxides, CO and unburnt hydrocarbons
► The urea removes the NOx
Issues
► The ‘cat’ is more efficient at higher temperatures
► CHP packages come supplied with ‘cats’ to meet local AQ requirements
► ‘cat’ manufacturers will not normally give performance guarantees for operating on feedstocks
derived from waste
► Urea injection is supplied as a package with the ‘cat’ giving reduced choice of configuration

15. Cooling the CHP Exhaust Gas
► CHP exhaust gases typically between 150 and 450oC
► Dangerously hot
► Valuable heat

16. Conveying the Exhaust Gas
► Need to ensure no back-pressure on the CHP
► Large diameter duct
► Expensive to build
► Expensive to insulate
► Compressor plus small diameter duct
► Cheaper to build
► Expensive to operate

17. Conceptual Design
BSAD
CHPs
Adiabatic Coolers
Exhaust
Treatment
and
Compression
Hot Well
Pump
Set
Greenhouses
Eco
nom
iser
Stack
Demand driven ‘waste-gate’ valve
and controls
1. 300kW compressor 0.42barg
2. Specialist catalytic converter
3. Dry urea injection
Optional economiser to recover
875kW from the exhaust gas as
hot water at 70 degrees
Two hours supply of hot water at
60 degrees.
300m3 insulated tank.
Normal operating temperature
70 degrees
200m of 500mm SS
insulated duct

18. Economics – Risk Free Scenario
For a 3.0Ha greenhouse
► Cost to grower of heat is £550kpa
► Supplier could charge £235kpa
► For a capex of £644k
► For an opex of £8kpa
► CO2 increases yield by 30% or more
► Worth at least £490kpa to the grower
► Supplier could charge £245kpa
► For a capex of £640k
► For an opex of £82kpa
► Supplier’s IRR of 12%
► Payback in 4 years
Many complex
interactions would
change these
figures

19. Wider Picture
Ten Water Company TH plants in UK
► Estimated waste heat of 24.5MW
► Enough heat for 25 to 50Ha of greenhouse
Food waste digesters
► DEFRA figures
► Currently 90MW of wasted heat
► Rising to 440MW by 2020
► Enough heat for 100 to 900Ha of greenhouse
► Four times current area
► 60% self sufficiency in tomatoes

20. Conclusions
Utilising waste heat and exhaust gases in greenhouses is practical
And viable
Heat demand is the key driver
And the limiting factor
Contact Details
Dave Auty: email: dave.auty@amec.com
tel: 113 389 1101

21. DEVELOPING BIORESOURCES
THROUGH AD
#UKADBiogas @adbioresources
CHAIR:
DR ADRIAN HIGSON, NNFCC
PANEL:
PROF CHRISTOPHER RAYNER, C-CAPTURE
STEVE BROOME, CPI
PHIL SCOTT, AMEC
JOHN WILLIAMS, ADAS UK
DR DONNA RAWLINSON, NORTHUMBRIA WATER