The high efficiency and flexibility of reciprocating engines makes them an attractive power source for district trigeneration (heating, cooling electricity) projects serving mega commercial spaces, eg, large office complexes, technology parks and new business districts.

Two recent Wärtsilä projects, one in India and one in Japan illustrate the possibilities.

Plug & play office space in India

International Tech Park, Bangalore (ITPB) – which has been described as the “IT hub of India” and currently accommodates 130 companies and a workforce of 20 000 – has pioneered dedicated technology parks in India, with fully ready to use “plug & play” office space and complete IT infrastructure. It also says it the first Indian business space to offer a “work-live-play concept”.

The 58 acre park, at Whitefield, 18 km from Bangalore, is an integrated and self-contained complex, including multi-storey offices, residential areas and recreational facilities. It has been developed by Ascendas of Singapore – corporate motto “We take care of your real estate needs so that you can concentrate on your core business.”

Construction of the park is being implemented in three phases, with total peak power demand for the three phases estimated to be about 9 MW, 21 MW and 24 MW respectively.

For Phase I, on which construction started ten years ago, a diesel captive power plant consisting of three 3 MW Wärtsilä engines was installed. A 3.4 MW Wärtsilä generating set was added in 2004, which was further augmented in 2006 with a 7.4 MW Wärtsilä machine.

It was during the planning stages for this latter engine that the concept of heat recovery and chilling was developed, by Ascenda and its consultants Tata Consulting Engineers.

It was decided to equip all four existing diesel gensets with exhaust waste heat recovery systems. The heat was also to be recovered from the new 7.4 MW engine’s cooling water system.

Since the park is fully air conditioned the heat recovery was primarily designed to provide the heat source for chilled water production from absorption chillers, employing lithium bromide solution as absorbent.

Two-stage absorption chillers, each with a capacity of 1250 TR (TR = tonne refrigeration = 3.5163 kWt), were installed and fed with high temperature hot water from four heat recovery systems added to the exhausts of each of the existing engines. The system was designed to reduce the temperature of the final exhaust stream from 350˚C-380˚C to below 200˚C in the interests of reduced environmental impact and maximising equipment life, with a lessening of ground level emissions concentrations and avoidance of acid formation by not allowing temperatures to fall too low.

A common high temperature hot water header was installed, to which each 1250 TR chiller is connected in parallel.

One of the 1250 TR chillers was also designed to accept additional low temperature heat in the form of high temperature jacket water from the new 7.4 MW genset.

Before the chiller retrofit the existing 3 MW gensets were operating at an electrical efficiency of 41.2% and the fourth, 3.4 MW, machine at 42%. Adding the chillers has increased efficiency by about 15 percentage points.

The new 7.4 MW genset had an efficiency of 43% and the incorporation of the chiller into its cooling circuit increased efficiency by 24 percentage points to 67%.

The efficiency of the entire four unit power plant, which is operated and maintained by Wärtsilä, under contract with Ascenda, is now over 60%.

The success of the Bangalore project has prompted another IT park developer, this time in Chennai, to similarly integrate chillers in a new 10 MW HFO fuelled plant that will consist of two Wärtsilä 2.6 MW gensets and one 5.2 MW machine.

And, with the burgeoning demand of the Indian software sector for high quality business space, coupled with growing needs for reliable power, cooling and heat, other similar trigen projects are likely to follow.

Trigen at Makuhari New City

In the Bangalore case chilling has been added to power generation. But at Makuhari in Japan, Tokyo Gas subsidiary EnergyAdvance has arrived at trigeneration from rather the opposite direction: it has added power generation to existing heating and cooling services.

Makuhari District Heating and Cooling Centre (MDHCC) was established in 1989 to serve the needs of companies in the 150 acre business area of Makuhari New City, which is roughly halfway between the centre of Tokyo and Narita airport. The MDHCC is fuelled with natural gas and provides steam at 170°C and chilled water at 6.5°C via a network of district heating and cooling pipes (installed in purpose built culverts under the city). The network serves customers such as the convention centre, hotels and office buildings.

The MDHCC has three furnace flue boilers generating steam at 0.8 MPa and two water tube boilers producing steam at 4 MPa. It also has an absorption chiller, which uses the 0.8 MPa steam, and a steam turbine driven turbo chiller that runs on the 4 MPa steam.

With an eye towards implementing what it calls the “microgrid” concept at some stage in the future, EnergyAdvance decided to add power generation to its offerings in Makuhari and to construct there a new facility consisting of two high efficiency gas-fuelled gensets plus yet two more chillers, one of the hot water absorption type making use of engine cooling water for its heat source and the other an electrically driven turbo chiller. This new tri-generation facility was taken into operation in March 2007

The two new gas engines are an 8.730 MW Wärtsilä W20V34SG, with an electrical efficiency of 45.6% (LHV) – the first such machine in Japan – and a 6.970 MW Wärtsilä 16V34SG, electrical efficiency, 45.5%.

The engines are equipped with exhaust waste heat recovery boilers, which are used to supply 0.8 MPa steam to the existing steam absorption chiller and to the district heating network.