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Belgian Tomato Grower Slices Energy Costs

The Tomato Magazine
August 2006

SINT-GILLIS-WAAS, Belgium – The renovated and expanded tomato-growing business belonging to Geert De Breuck includes a covered area of more than 27,000 square meters (six acres), making it a large business for the region of Sint-Gillis-Waas (Belgium). The facility produces about 1,650 metric tons (3.64 million pounds) of tomatoes annually with the help of an innovative combined heat and power (CHP) system designed and manufactured by Cummins Power Generation. The system uses natural gas to generate electricity, heat and carbon dioxide which are all used to accelerate the growth of the tomatoes.

The CHP system is the result of a direct partnership between the grower and Cummins Power Generation. Cummins provided the equipment and technical expertise for the CHP system as well as the bulk of the financial investment. With a power system that operates above 90 percent overall energy efficiency, as well as government regulations that grant CHP certificates and CO2 emission permits, the project is proving to be very economical.

Power system components
The centerpiece of the CHP system is a Cummins Power Generation model GQMB 1.5 MWe lean-burn gas generator set. The generator is powered by the Cummins QSV91G natural gas engine that has developed an enviable reputation for high thermal efficiency, low exhaust emissions and high reliability. The generator produces electricity that is mainly injected into the grid; less than five percent is used on site.

Waste heat from the generator set’s water jacket and exhaust are recovered via a heat exchanger and used to provide heat for the covered plant-growing areas year round. A large buffer water tank was designed to store heat produced during daylight hours. The heat can then be released during the night to keep the plants warm. In addition to producing heat, the generator’s exhaust gases are also a source of carbon dioxide that the plants need for photosynthesis. A special exhaust gas washer is employed to cleanse the exhaust before the carbon dioxide is used to encourage plant growth. The system is housed in a prefabricated concrete building measuring 11 x 12 meters (36 x 39 feet) which provides ample room for maintenance.

Optimizing operation was a key to success
Optimizing the operation of the CHP system was a key to its economic success, but this was often complicated by the needs of the growing plants and the realities of operating a generator set. During daylight hours in the summer, for example, the tomatoes need ample carbon dioxide but require little additional heat. A CHP installation is better suited for providing the carbon dioxide than a traditional gas-fired boiler, however.

While a CHP installation supplies only half the amount of heat per cubic meter of gas compared with a gas boiler, it produces an equivalent amount of carbon dioxide – plus electricity that can be used on site or sold to the local utility. By only running the CHP system during daylight hours, it produces carbon dioxide when the plants need it, and generates electricity when its value is the highest. When heat is needed during the night, hot water is circulated from the large buffer tank that was warmed by the system during the day.

Other factors were also important to making the installation profitable for the grower, namely system design, system efficiency and system availability. In order to make the system economically feasible, the design team calculated that the system had to operate between 4,000 and 5,000 hours annually – or a little more than half of all the available hours. This required that the generating system have an extremely high availability factor in addition to having a sufficiently large heat-storing buffer tank to make efficient use of the waste heat from the generator. Another key to the success of the system was the exceptionally high overall efficiency of the Cummins Power Generation generator and the heat exchangers. Compared with producing heat and electricity separately, the CHP system realizes an energy savings of about 25 percent.

Projected payback period of 3.5 years
While the financial performance of the CHP system depends on a number of factors – the price of tomatoes, the price of natural gas, the value of the electricity sold, the value of the government CHP certificates and maintenance costs – the optimized system was designed to pay for itself in about three and one half years. Gas prices tend to fluctuate, but the selling price of electricity can be negotiated for up to three years. At current gas prices, the sales of electricity alone pay back a major part of the cost of the consumed natural gas.

For more than 80 years, Cummins Power Generation has been a major force in increasing the availability and reliability of electric power around the world. Its extensive global distributor network delivers innovative power solutions for any on-site power need from remote prime power systems, to clean, energy efficient cogeneration systems, to waste-to-energy power systems that extend our natural resources. For more information on waste-to-energy power systems, contact Guido Taymans, 1-877-769-7669 (US) or +44 1843 25500 (UK); by e-mail: energysolutions@cummins.com. Or visit www.cumminspower.com/energysolutions.

© 2006 Columbia Publishing

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