Page 62 - Energize November 2021

TECHNICAL

Clarke Energy and AGR opted for an ammonia (R717) refrigerant system as opposed to Energy usage in glasshouses
a hydrocarbon refrigerant from IES Energy as ammonia has a higher efficiency value and a The energy created by gas engine combined
global warming potential of zero. heat and power systems in glasshouses can
be used in various ways. The electricity can
Client AGR Renewables provide the power for the artificial lighting
and/or be fed into the electricity grid. The
Engine output 9 MWe
heat efficiently meets the glasshouse’s
Heat pump output 33 MWth
requirements. In addition, the climate
Location Chittering, Cambridge, UK
relevant CO 2 of the engine exhaust gas
Engine manufacturer INNIO Jenbacher, KOHLER SDMO
serves as a fertiliser for the plants.
Heat pumps IES Energy / Pure Renewables
Installation Clarke Energy Exhaust purification
Engine types Jenbacher J416, J620 and J624 After the purification of the exhaust gas
Primary fuel: Natural gas with special catalytic converters (SCR and
Table 1: Project overview oxidation catalytic converters), the exhaust
gas is cooled down by a heat exchanger
Liquid-to-water heat pumps recover renewable heat from local reservoirs on site via to approximately 55°C and supplied to
the reverse Carnot cycle and through the use of an ammonia refrigerant. The open-loop the glasshouse for CO 2 enrichment. A
collection system involves eighteen pumps floating on platforms spread across the three measurement device that constantly
reservoirs, which will extract water from the reservoirs and transfer any available heat to measures the exhaust gas levels ensures
the ammonia refrigerant (approx. 10°C). maximum safety for vegetation.
The heated ammonia is pumped to seven compressors located near the glasshouse The CHP plant will consist of Jenbacher
where the ammonia is compressed, and heat is transferred to the site’s thermal stores at J416, J620 and J624 engines providing an
about 50°C. The compressors are divided into three separate, skid mounted systems, one electrical output of 9 MW, which will be
single compressor (4,7 MW) and two twin compressors (9,5 MW), powered in part by the used to power the glasshouse, the LED
Jenbacher engines. “grow lights” and various site auxiliaries.
The waste heat generated from the engines
CO 2 from CHP engines and plant growth is to be used to heat water, which will be
Plants grow by converting CO 2 to carbon through photosynthesis. Air generally contains stored in two 6000 m thermal stores for
3
approximately 350 ppm CO 2. Optimal CO 2 levels depend on the type of plant and heating the glasshouses. The CO 2 recovered
generally lie above 700 ppm. With increased artificial lighting, as present in glasshouses, from exhaust gases will be transferred
plants absorb even more CO 2. If the greenhouse atmosphere is enriched with CO 2, the to the glasshouse to help accelerate the
temperature kept on a constant level and enough lighting provided, plant growth and, growth of the produce. n
consequently, the harvest yield can be increased significantly. When burning natural gas
in gas engines, approximately 0,2 kg CO 2 is produced per kWh of energy input. This CO 2 is Send your comments to
present in the exhaust of gas engines in a concentration approximately 5 to 6% by volume. rogerl@nowmedia.co.za

Contact Mark Yelland for all your advertising requirements:

Cell: 074 854-1597 | Email: marky@nowmedia.co.za

energize | November/December 2021 | 60