High overall efficiency thanks to cogeneration of heat and electricity
The number of plants based on the principle of cogeneration has been increasing in Latvia since 2000. The Central Statistical Bureau of Latvia registered 71 CHP modules in 2009, and nearly twice as many (133 modules) just three years later. Eleven of these are located in the southwestern section of the country in the city of Daugavpils, where they are operated by the Estonian mtu distributor Baltic Marine Group (BMG). Their main task is to ensure the municipal heat supply for the city. One of the modules is also in service for an industrial customer from the railway sector, which uses the selfproduced heat and electrical energy right in its own facilities. Planning and engineering services for construction of the plants were rendered by BMG, which also provided boilers to handle peak loads as well as heat exchangers for extraction of the exhaust heat. The heart of the plants came from mtu: Each module consists of a mtu Series 4000 gas engine, a generator and an MMC module control unit (MMC stands for mtu Module Control). A heating module is used to draw heat from the engine cooling water, which can be up to 90°C, and then feed it into the district heating network.
In addition to heat, the modules are continually generating electrical energy via a generator driven by the gas engine. This energy can then be fed into the public power grid by the end customers. In order for this to occur, the Latvian Energy Act requires the system to have an efficiency level of at least 80% per year—a requirement that the power plants are easily able to fulfill thanks to their overall efficiency rate of nearly 88%.
Reliable heat supply as a complete solution
As the general contractor, BMG supplied the entire cogeneration systems from a single source. The first two went to the municipal heat supply company Daugavpils Siltums in 2010. The company had its increasingly uneconomical boiler houses replaced by modern CHP systems based on mtu gas engines of Type 12V 4000. A total of eight such generator sets at two locations produce the energy necessary to supply some 4,500 households—8,000 kilowatts of heat energy (kWth) and just under 8,000 kW of electrical energy (kWel). mtu even electronically reduced the possible output of each engine from 1,165 kWel to 999 kWel in order to ensure the higher remuneration for systems with an output of under 1,000 kWel. Each of the generator sets has meanwhile run for over 10,000 operating hours. „The gas engines were developed and optimized by mtu for continuous operation under full load,“ explained Ivan Kilter, CEO of BMG. „They are particularly efficient and economical for generating heat and electricity in cogeneration plants. Our customers were equally convinced.“
BMG commissioned two additional plants for the heat supply company in mid-September 2013. At a site outside of the city, two generator sets of Type GR 1999 N5 supply 2.2 MW of heat and 1,999 kW of electricity. The anticipated service profile made it worthwhile to equip the cogeneration plants with larger engines. In contrast to the systems with twelve-cylinder engines that do not always operate at full power —such as during the summer—and are turned off when less output is required, the larger generator sets operate around the clock throughout the entire year. In combination with peak load boilers, this enables BMG to respond more flexibly to the need for heat, such as when frigid subzero temperatures are replaced by a mild thaw during the heating period—which can happen within a single day.
Fuel-efficient and future-proof design
Because it lacks fossil raw materials, Latvia is dependent on Russia for imports. Low fuel consumption therefore plays a key role, especially in the energy supply. “The new plants require significantly less natural gas to generate the same amount of heat as the old boiler houses did,” underscored Ivan Kilter. Thanks to full heat extraction of exhaust gas and engine heat, the CHP modules make the most thorough usage possible of the energy contained in the fuel, which is the clue to their exemplary overall efficiency rate. “The solution pays off for our customers within just three to four years as a result of the high energy efficiency rate.”
Added to this is the fact that the new systems enable the heat supply companies to finally put an end to the safety risks posed by the aging heat boilers. Because that type of equipment is no longer made, competent maintenance staff is increasingly hard to find—as are the appropriate spare parts. In the case of an emergency with the new plants, BMG can rely on the expertise of the mtu service staff. BMG handles simple jobs such as measuring oil levels or replacing certain components itself and leaves complex tasks—such as replacing wearing parts or checking and reworking engine components —to the team from mtu. Plans are already in place for the general overhaul of the equipment in approximately eight years after some 63,000 hours in operation. Instead of completely removing, reconditioning and reinstalling the used engine—a process that can take up to three months, during which the equipment is inoperable—Daugavpils Siltums will sell it back to mtu and receive a structurally identical Reman engine. This is an engine that has been thoroughly examined and completely overhauled by mtu following a standardized procedure, and is thus almost as good as new.
Industrial company saves up to 50% of energy costs
In addition to the CHP modules belonging to the heat supply company, BMG operates another system located on the grounds of a Latvian locomotive manufacturer. This system is based on an mtu gas engine of Type 16V 4000 and produces enough heat (1,719 kW) and electricity (1,560 kW) to cover the requirements for industrial processes, heating and lighting. The manufacturer relies on the public power grid only to cover unforeseen load variations. “The new equipment enabled our customer to significantly reduce its energy costs,” explained Ivan Kilter. “Ultimately, the company pays only half as much for the electricity it produces itself.”