There is always an element of calculated risk in being among the first customers for a new generation of engine. But the hope of course is that this will be outweighed by the benefits of the new technology. This has certainly been the case for Cogetherm's new combined heat and power (CHP) plant at Peugeot's Mulhouse factory, which uses ten CW12V220 engines running on natural gas.

One of the new breed of industrial cogen projects currently proliferating in France, the Peugeot CHP installaton at Mulhouse is the biggest and most complex such plant yet put in operation by Cummins Wärtsilä (also based in Mulhouse). It builds on experience with an 8 MW pilot installation (owned by Siif Energy) that has been operating for a couple of years at Cummins Wärtsilä’s own factory to test out the details of the cogeneration process.

On 1 November the 20.4 MWe / 16.7 MWt Peugeot Mulhouse CHP plant (pictured above) entered its second season of operation, following the seven month summer shutdown. In the first season, 1 November to 31 March 1999, performance was generally in line with contractual requirements, which stipulate 3624 hours of non-stop electricity, hot water and steam production. The production figures for this first season were 64 760 800 kWh of electricity, 16 933 700 kWh of steam, 25 821 300 kWh of hot water, with a gas consumption of 17 503 610 Nm3.

Nevertheless there were initial difficulties caused by oil and additives in the gas supply. Fins and tubes in the exhaust gas heat exchangers became coated, which meant the plant had to be stopped for cleaning. The source of the oil was a pumping station in the gas supply line several km from the site.

Solutions included installation of modified heat exchangers, employing smoke tube technology, and the fitting of oil filtration systems on each engine, which can be cleaned while the plant is in operation. A benefit of having ten engines was that despite these teething problems, the required production levels were met because while some engines were being cleaned others could continue to operate.

Considering the options

The Peugeot car manufacturing plant in Mulhouse, France, is one of the main production sites of the PSA Group and the largest industrial facility in the Alsace region. The plant is dedicated to production of the smaller models, the 104, the 205 and now the 106 and 206. It produces 1600 cars a day and employs some 10 000 people.

Intense competition in the motor industry is causing the leading players to focus increasingly on their core business. PSA therefore decided to outsource heat production at Mulhouse, at the same time looking to make the facility more comfortable for the workforce, reducing emissions and lowering energy costs.

The plant is a major consumer of process steam heat, for painting, and hot water, for space heating, in one of France’s coldest regions. To meet its objectives Peugeot sought an operator who could provide an integrated service that would eliminate investment cost burdens and operating risks.

EDF subsidiary Cogetherm proposed a cogen plant with a 12-year heat supply contract, guaranteeing substantially reduced energy costs – some EUR 600 000 per year. All the electricity produced by the CHP plant is sold to EDF via the 63 kV grid, while the car plant’s own electrical needs continue to be met by EDF through the national grid. The basic role of the new plant is thus to provide heat by burning gas in reciprocating engines and to offset the costs of doing that by selling cogenerated electricity to EDF. The seasonal operating regime (3624 hours, November-March) is adopted to gain maximum benefit from the high electricity prices that apply in the five winter months – 85 euro/MWh, compared with 28 euro/MWh in the period April-October.

Cogetherm has full responsibility for financing, construction and operation of the CHP plant. In turn Cummins Wärtsilä, a joint venture of Cummins and Wärtsilä NSD set up to address the diesel and gas engine market in the 1-4.5 MW size range, was awarded the turnkey contract for design and construction of the plant, as well as for O&M over 12 years, with a performance guarantee to Cogetherm.

The plant configuration selected consists of ten natural gas reciprocating engine gensets with high electrical efficiency, 41 per cent, and low NOx emissions. The plant has a constant power output of 18.3 MW and a heat output of 16.5 MWt. The overall efficiency of the plant is 72 per cent.

Some of the existing boilers are being kept in operation to supplement the cogeneration plant during peak periods. The new CHP plant is installed 20 m away from the existing boiler house.

Gas turbines were considered but in the end it was decided to opt for reciprocating engines. The competitive advantage of reciprocating engines derives from their higher electrical efficiency. For a given set of conditions and with the same natural gas consumption, the electric power produced by reciprocating engines is greater than that for turbines, resulting in increased revenues from electricity sales and therefore a better rate of return compared with technologies having lower electrical efficiencies. Also, reciprocating engines require a lower gas feeding pressure (4 bar versus 15 bar for turbines). Therefore no gas compressor is needed, with a saving of about FF 1 million per engine (compressor maintenance costs not included). Last but not least, electricity consumption by auxiliaries (generally deducted from the electrical power plant production) is drastically reduced.

Initially Cummins Wärtsilä, working with another investor, made a direct offer to Peugeot, but Peugeot preferred a joint venture with Cogetherm on the grounds that this would make it easier to manage the electrical power supply contract with EDF following completion of the cogeneration plant – Cogetherm being a subsidiary of EDF.

Other factors prevailed at Peugeot’s Sochaux site, where turbines were recently selected for the Cogetherm CHP installation to be constructed there.

Plant design

Among the key design features of the Peugeot Mulhouse CHP plant are low emissions (70 per cent TA Luft as of January 2000), minimum noise (achieved by indoor installation with individual sound-proofing enclosures for each engine), ease of maintenance and advanced control and monitoring systems. Since the plant was installed its emissions have been progressively lowered to meet the January 2000 limits. Measures have included new turbocharger specifications and adjustments to combustion electronics.

The engines’ cooling systems are used to provide the heating for the hot water, via two heat exchangers.

The ten engines share a single heat recovery steam generator, which uses exhaust gas to produce steam and, by means of a further heat exchanger, preheats the hot water.

The cogeneration plant has been designed for unmanned operation. Consequently, the existing boiler plant has been fitted with a state of the art control system and the whole plant can be remotely operated.

There are several levels of control on the power plant. The first level is engine control, which uses WECS (Wärtsilä Engine Control System). The second level consists of the genset control panel (GCP) and the power station control panel (PSCP).and is based on Klockner Moeller PLC technology. The third and final level is the supervision system, which uses monitorTM software.

WECS is a physically distributed system consisting of four types of unit located at various points on the engine. The four different units, all of which can communicate with each other over a local CAN-bus, are:

  • The MCU (Main Control Unit): This controls performance through combustion process parameters and integrates speed/load control, ignition timing, and monitoring/safety.
  • CCU ( Cylinder Control Unit): There is one CCU per two cylinders, and for each cylinder the CCU controls one ignition module, two solenoid valves (the main combustion chamber valve and the pre-combustion chamber valve). It also measures the exhaust gas temperature for each cylinder.
  • DCU (Distributed Control Unit): This measures and converts analogue and binary sensor signals to digital data, which are then transmitted to the CAN-bus.

KDU (Knock Detection Unit): This measures signals from accelerometers mounted on each cylinder head. These signals are filtered, amplified, converted to digital form and sent to the CAN-bus.

The GCP is for startup and shutdown operations as well as for synchronising and parallel sequencing of the set circuit breaker. The panel includes generator protection and genset auxiliaries management. Operation of this system is manual, semi-automatic or fully automatic. The GCP is directly connected to the WECS by a Profibus Network.

The PSCP manages the entire power plant, controlling grid connection, auxiliary systems and safety systems. It includes: the decoupling protection panel (which prevents unwanted grid connection under fault conditions and also ensures that the various consumers connected to the power plant have the required voltage/frequency characteristics); the steam boiler control panel (allowing all engines to be stopped should a problem with the boiler arise); and the fire and gas detection system. The system allows engines to be managed individually or all together.

In addition, the PSCP concentrates all information coming from the GCPs and the power plant as a whole for the supervision system. The supervision system allows the operator to see historical trends for all kinds of information, as well as current values and lists of alarms.

The supervision system can be accessed remotely via the telephone network, allowing remote surveillance of power plant performance and engine behaviour (eg, by the O&M department of the power plant supplier).

Future prospects

Other CHP projects involving the Cummins Wärtsilä V220 engine are currently underway. These include Coca Cola, Brazil (2xCW12V220), FTOF textile factory, Portugal (2xCW12V220), Waterford Crystal, Eire (1xCW12V220) and Stadtwerke Tubingen, Germany, where a district CHP plant with four of the 18 cylinder engines (4xCW18V220) is under construction.