Providing power and critical temperature control to year-round greenhouse operations demands high quality equipment capable of delivering exact specifications to ensure maximum growth potential in plant life. A stout standby power system is also important to guarantee little to no loss of power is experienced during delicate agricultural applications.
|On-site power generators can be used in greenhouses, meaning they can produce tomatoes and aubergines even in Belgium|
The Eric van den Eynde Greenhouse cultivates around 1.2 million tomatoes and one million eggplant crops each year at its 4 hectare (9.8 acre) facility located in Kontich, Belgium. The greenhouse, 20 km north of the Belgium capital of Brussels, needed an on-site power generation system to provide combined heat and power (CHP) to maximize growth of the vegetables. The conservatory must maintain a temperature of 20°C for prime growing conditions; specific additional amounts of carbon dioxide are also desirable in this process. A reliable method of providing heat, electricity and gas will maintain business,and accelerate plant production.
|The new, 2 MW gas-fuelled genset installed at the Eric van den Eynde Greenhouse in Belgium|
While the greenhouse is connected to the local utility, IMEA, on-site CHP generation with carbon dioxide enhancement was required. A CHP system was an attractive solution to energy needs, as the majority of power generated could be sold back to the local utility IMEA to increase the overall return on investment.
UNIT PROVIDES ENERGY AND CARBON DIOXIDE
An engineering evaluation by Eneria, the local Caterpillar dealer, determined that the greenhouse would be best served with a new generator set to replace existing Cat equipment that had been used as the main source of power since 2001. Previously, two Cat G3516A generator sets rated at 1070 kW provided the conservatory’s needs. A Cat G3520E natural gas module rated to 2070 kW was installed in 2007 to serve as the main power source and CHP.
The G3520E is housed in an enclosure separate from the greenhouse itself while the existing units are located in an engine room inside. Controls for all three units sit next to the interior engine room for on-site monitoring. The modules can also be monitored remotely. These controls allow running hours of generator sets in the greenhouse to be adjusted everyday depending on hourly changeable electricity costs.
Only 5% of the electrical power produced by the G3520E is consumed by the greenhouse. The remaining 95% is sold to the local utility IMEA. An internet-based exchange market for electric power in place in Belgium allows electricity producers to sell power instantaneously. Electricity costs can change on an hourly basis so running hours of the generator sets are adjusted on a day-to-day basis via the generator sets’ controls to take best advantage of power and prevailing rates from IMEA.
The heat portion of the CHP installation comes in the form of hot water and is used to stabilize the greenhouse temperature at the desired 20°C. Water with a temperature of 95°C is stored in a 1200 cubic meter boiler while water at 45°C runs in metallic tubes surrounding the greenhouse. The temperature is maintained between 19°C-21°C (66°F-69°F) throughout the year.
In addition to hot water, waste steam is used to power absorption chillers fuelling the greenhouse’s cooling system. This supplementary recovered heat eliminates the need for extra boilers and contributes to the efficiency of the plant.
The typical electrical output of a gas engine is about 41% of total fuel gas energy input. More energy is recovered from an engine by capturing the heat from the aftercooler, the engine jacket water, the cooling oil water and exhaust gas. This allows the greenhouse to recover around 90% of its total input energy.
The exhaust gas from the generator sets are cleaned of nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons (CnHm). Selective catalytic reduction (SCR) and oxidation systems convert these gases to cleaned forms before they are allowed to re-enter the air outside. Carbon dioxide is re-introduced into the greenhouse. The gas is supplied for 12-16 hours per day during summer months and six hours per day during winter months. The generator set produces 240 kg of carbon dioxide per hour per hectare. Because the greenhouse requires only 180 kg of carbon dioxide per hour per hectare, nearly 75% of the gas is captured and recycled.
‘I chose a CHP solution because it allows me to run my greenhouse in a good financial condition,’ Eric Van Den Eynde, the greenhouse owner, notes. ‘We get our power, heat and all of our supplements for our plants from one machine, and we also get the additional benefit of being able to sell our electricity to the grid.’
Without the CHP installation liquid carbon dioxide would be needed for the greenhouse year-round at a cost of nearly €100 per liquid tonne. Around 180 kg per hectare of carbon dioxide are needed on an hourly basis. With Caterpillar generator sets, carbon dioxide becomes available as a free by-product. Harnessing the electricity, heat and carbon dioxide, the Eric van den Eynde Greenhouse capitalizes on all facets of its power generation. By utilizing the full scope of the cogeneration plan, the facility is able to meet its economic goals as well as its environmental goals.
The financial return for such a power station investment is approximately three to four years by the heat recovered from the engine through water and exhaust gas recovery instead of gas-fired boilers, the excess electrical output from the gas generator sold to the local utility, and the carbon dioxide fertilization by using exhaust gases of the engine.
‘Our Cat G3520E module provides all of the things our plants need to grow and helps us run a successful business,’ Van Den Eynde says.
The G3520E advanced, gas-fuelled generator set
The G3520E advanced, natural gas-fuelled generator set from Caterpillar is designed for maximum efficiency in extended-duty distributed generation and CHP applications.
Driven by an electronically-controlled, lean-burn gas reciprocating engine and operating on the Miller Combustion Cycle, the G3520E generator set delivers up to 44.5% mechanical efficiency. It provides flexibility to operate on pipeline natural gas with a wide range of methane numbers, without sacrificing efficiency and performance.
The 20 cylinder G3520E generator set operates at 60 Hz/1200 rpm, is rated at 1600 kW, and has a standard NOx emissions rating of 1.0 or 0.5 g/bhp-hr. It is built on a heavy-duty diesel-based platform and uses an advanced camshaft and turbocharger design to achieve high mechanical efficiency. It additionally features a low-pressure fuel system 10 to 35 kPa.
R&D on engine for CHP
Gas- and, less frequently, liquid-fuelled reciprocating engines are one of two main prime movers used for CHP plants around the world, the other being gas turbines. Engines have been around for a long time and R&D progress in this area does not move fast.
Finland’s Wärtsilä is one of the companies driving a national three-year combustion engine technology research programme established by a consortium of Finnish technology companies and research institutes. The principal aim of the Future Combustion Engine Power Plant (FCEP) programme is to develop reciprocating engine and related power plant technologies to ensure that Finnish industry can maintain its leading position in global markets, while meeting the requirements of tightening environmental legislation. The project also enables closer co-operation to create synergies between the research activities of the consortium members.
The programme, which is being led and co-ordinated by CLEEN Oy, the Strategic Centre for Science, Technology and Innovation of Finland, is scheduled to be completed by the end of 2012. Key areas of research include improvements in the combustion process, energy efficiency, emissions reduction methods, heat recovery systems and power conversion technologies. Fuel flexibility and the use of biofuels in combustion engines are also to be amongst the central areas of research.
Meanwhile, in the US, and with the US Environmental Protection Agency’s Tier 4 Interim and European Stage IIIA off-highway emissions regulations approaching in January 2011, engine manufacturer Cummins is at the forefront of efforts to meet tight new standards for off-highway emissions with its G Drive series of engines. The new breed of Cummins engines, which were first shown at the Power-Gen International exhibition last December, meets regulatory standards and is designed to deliver all its performance advantages without incurring higher operation costs.
Cummins says that its commitment to investing in research has enabled its engineers to develop one of the world’s most advanced range of engines that delivers both increased fuel efficiency and reduced emissions.
Since the introduction of non-road Tier 1 regulations in 1996, the EPA has incrementally lowered the limits on emissions from diesel-powered, non-road equipment. Tier 4 regulations require diesel engine exhaust emissions that are significantly lower than previous tiers. For example, Tier 4 electrical power products will produce approximately 93% less NOx and 94% less particulate matter (PM) than Tier 1 products. Tier 4 regulations apply to both stationary and non-road mobile applications and are split into two parts, termed Tier 4 Interim and Tier 4 Final. The Interim phase begins in 2011-2012, with even more stringent limits to come into effect in the Tier 4 Final phase in 2013-2015.
Cummins achieved Tier 4 Interim emissions levels by developing engine combustion technology to work with the after-treatment filter in reducing PM emissions levels by 90%. The use of cooled exhaust gas recirculation (EGR) enables the required 45% reduction in NOx to be achieved. Engine enhancements also include the use of Cummins ‘Variable Geometry Turbochargers’ (VG Turbo), advanced electronic controls and high pressure common rail fuel systems.
Lubrication engineering gives another route to improving engine performance. ExxonMobil has launched its Mobil SHC Pegasus series of advanced technology oils designed to maximize natural gas engine component reliability, but with additional energy efficiency opportunities. Developed for optimum engine protection in natural gas engines, the series exhibited average energy savings of up to 1.5% in independent laboratory testing and field tests.
The new Mobil SHC Pegasus formulation delivers the potential for reduced fuel consumption, increased oil drain intervals, and exceptional engine cleanliness and component protection, says ExxonMobil. Controlled field testing in demanding gas compression applications has shown that oil drain intervals can exceed 12,000 hours, or three to four times that of standard natural gas engine oils. Extending oil drain intervals can help reduce the amount of downtime the engine experiences as well as reducing the amount of waste oil generated.