Trigeneration plant: what it consists of and who supplies what

A trigeneration (CCHP) plant is a gas engine with a generator plus everything that turns its heat into cooling and rejects the surplus. The engine provides electricity and heat. Then the cooling circuit takes over: the heat recovery unit collects the heat, a lithium bromide absorption chiller turns it into cooling, and a cooling tower or dry cooler rejects what the chiller did not use. While the site has only an engine, it is cogeneration (CHP). The cooling circuit turns it into trigeneration.

How gas becomes electricity, heat and cooling

Gas goes into the engine. Electricity goes to the consumer, the jacket and exhaust heat goes to a Thermax chiller, which makes 7/12 °C water, and the heat of the chiller itself is rejected by an NCT cooling tower.

What parts does a trigeneration plant consist of?

There are seven parts, and the heat pump is not always needed. We also supply the first part, the engine with a generator: these are gas engine generator sets. It is selected for the heat and the load profile, and everything after it is the cooling circuit.

How much energy does the plant deliver?

From 1 MW of gas, the engine gives about 40 % electricity and 40–45 % heat, 80–85 % in total. That is about 400 kW of electricity and about 450 kW of heat. An engine without heat recovery uses 35–40 % of the fuel; the rest goes up the stack and into the radiator.

Where a megawatt of gas goes

From 450 kW of heat, a hot water absorption chiller with a coefficient of 0.8 makes about 360 kW of cooling. If you take the exhaust heat and give it to a double-effect chiller, the same heat gives twice as much cooling.

The COP is the ratio of the cooling produced to the heat consumed. For hot water chillers it is below one, and for double-effect chillers on exhaust, steam and gas it is 1.30–1.45. That is why the type of heating medium determines which chiller to install.

How do schemes differ by heat source?

The choice is driven by the heat temperature and what the site needs.

Details on each series: Thermax absorption chillers and exhaust-fired absorption chillers, Trigenie. Which scheme suits your engine, see the sections on gas engines and gas turbines.

How does the plant work through the seasons?

This is the main difference between trigeneration and cogeneration. In winter cogeneration uses engine heat for space heating, and in summer it dumps it to the atmosphere through radiators. In summer trigeneration sends the same heat to the absorption chiller and gets cooling. The engine is loaded all year round.

Where engine heat goes by season

In winter the heat goes to space heating, hot water and process needs. In the shoulder season it is split between heating and the chiller. In summer it goes to the chiller and gives 7/12 °C water. The site gets electricity all year round.

What happens when the engine is down? The grid connection remains as a backup, and the chiller can get heat from the boiler house: this is how the scheme with two heat sources works at a greenhouse complex in Sverdlovsk Region. An NCT chiller covers the peak and backs up while the absorption chiller reaches its operating mode, which takes about 30 minutes. More: NCT chillers.

Where does a trigeneration plant break down?

Most often between the machines. Six places where mistakes are made: exhaust back pressure, engine jacket overheating when the chiller stops, return temperature, engine load and cooling demand out of step, crystallization on power loss, and untreated cooling tower water.

Each of them lies on the boundary between the engine and the cooling circuit. If they are split between different contractors, the interface belongs to no one, and a mistake there turns into a dispute. That is why it makes sense to give the gas engines, the cooling circuit and the interface between them to one company. A breakdown with figures: why trigeneration does not pay back.

What does Cold Energy (NCT) supply?

You can order gas engines, the cooling circuit and the interface between them from one company: gas engines, Thermax absorption chillers, NCT cooling towers, dry coolers and chillers, pump skids, water treatment and controls. For the cooling circuit we handle design, supply, installation supervision, commissioning and service. The company has been operating since 2011 and is the official representative of Thermax in Russia and the CIS. In Russia and the CIS, Thermax chillers are supplied only by Cold Energy. We calculate the engine and the cooling together, because the exhaust and the jacket determine which chiller will be installed.

Sites where our chillers work with gas engines and turbines are described in the Projects section: the Syry Kubani cheese plant, the Teplichnoye greenhouse complex, Mikran and many others. More on NCT equipment at nc-t.ru.

How do you know you need such a plant?

Four questions. Is there gas and a gas allocation. Is electricity expensive, or can the grid not provide the capacity. Are heat and cooling needed for at least 3,000–4,000 hours a year. Is the cooling load above 300 kW. Four "yes" answers mean trigeneration is worth calculating. Below 2,000 hours a year an absorption chiller does not pay back.

You can request a feasibility study for your site, and a quick estimate is available in the calculator.