Servicing of CAT gas-fired cogeneration units

In response to questions that arise, regarding servicing (maintenance) of gas CHP (Combined Heat and Power) units, I have decided to familiarise you with the issues/topics related to servicing and the scope of servicing. Having worked at Eneria for several years, I have been professionally involved in planning maintenance, overhaul and pricing of parts and services related to gas cogeneration in the broad sense. We are currently drawing up in-service maintenance plans for Caterpillar gas engines that are in our service and those of external clients. After buying engine manufacturer MWM, then owned by DEUTZ, Caterpillar in its service has gas engines (gas-fired cogeneration units) with electric power in the range of 400-4,500 kWe.

The specifics of servicing gas CHP units are closely related to where they are installed, i.e. the type of gas that is used to power them. We are currently service units that run on the following types of gas:

• Type E high-methane natural gas  (formerly GZ – 50) – local CHP plants and on-site CHP plants,
• LNG gas – local CHP plants and on-site CHP plants without access to natural gas from the transmission network,
• biogas – depending on the type of biogas, their typical locations are agricultural biogas plants, municipal landfills, municipal and company wastewater treatment plants,
• waste gases (coke oven gas) – coking plants,
• mine gas captured by underground facilities – trigeneration systems to produce electricity, heat and cooling for mine air conditioning systems,
• with natural gas extracted from coal deposits after the coal deposits have been fractured from the surface – the local CHP plant in Gilowice is a pilot and unique installation of PGNIG in Europe.
• raw natural gas in natural gas mines – compressor systems powered by gas engines.

Despite the obvious association of CHP systems with combined heat and power generation, gas-fired cogeneration units are also used to create the right atmosphere in greenhouses during CO2 fertilization in crop production. For this purpose, exhaust gases from CHP engines are purified and injected into the greenhouse.

Another way to use gas-fired CHP systems is gas-fired trigeneration.  In these systems, heat is used to produce utility cooling in absorption equipment.

How often is it recommended to service CHP units?

Depending on the gas fuel used, the biggest difference in servicing is seen in the timing of periodic inspections of gas-fired CHP units. This is due to the many aspects of using different types of gases as fuel. In this entry, I will only mention two aspects. They are related to the different methane numbers of the various gases and thus their tendency to knock combustion, as well as their physical and chemical composition, where various physical and chemical impurities are very often present as ballast. They cause faster wear and tear and the formation of combustion deposits in the chambers of individual cylinders and components located therein, such as valves and spark plugs.

 

Image no. 2

Image no. 2 shows the head removed from a TCG2016 cogeneration unit running on biogas. There is visible wear on the valve seat and valve itself. Image no. 3 shows the measurement of the height of the valve stems.

The longest intervals between inspections occur in combustion engines powered by clean natural gas, then engines powered by biogas from agricultural biogas plants and engines operating on waste gases, and finally cogeneration units powered by landfill gas, where, despite the use of the most advanced gas purification systems, impurities in the gas are simply the most abundant.

According to many, “servicing of gas CHP systems” begins with the arrival of a service bus with Eneria service technicians to the facility/location where the CHP system is installed – Image no. 3. In fact, the maintenance of gas CHP systems, is not just an occasional presence of the service technician at the unit, but a process of continuous supervision of the technical efficiency of the generator. It consists of:

• daily (continuous) verification of the unit’s operating parameters,
• daily inspection of the unit and organoleptic verification,
• removal of simple faults and failures by the operation of the CHP system,
• inspections and repairs performed by the service of the engine manufacturer’s representative,
• scheduling of inspections to be performed by the service of the manufacturer’s representative.

Service planning is very important due to the continuous nature of the CHP unit’s operation and the need for high availability.

Why is it worth using the Eneria cogeneration unit service?

Cogeneration units usually operate over 8,000 mth per year (with no intermediate inspections in a given year, images 5 and 6, and major inspections that take place every few years, photos 7 and 8).

 

Image no 4.                                                                     Image no 5.

Image no6.                                                                     Image no 7.

Carrying out scheduled maintenance and repairs is very important in terms of the reliable and continuous operation of CHP units. Performing scheduled maintenance work minimises the downtime of CHP units in every case (image 9).

Image no 8.                                                                      Image no 9.

This is related to preparation in terms of picking the necessary parts, the right number of mechanics, and reserving the necessary time with subcontractor companies to carry out the planned scope of work. This may include performing service on the turbocharger (images 11 and 12), dynamo (images 13 to 16)

 

Image no 10.                                                                          Image no 11.                            Image no 12.

Image no 13                                                                         Image no 14.                                  Image no 15.

 

Image no 16.                                   Image no 17.

or cleaning heat exchangers (images 17 and 18), and emergency coolers (image 19).

Image no 18.                                                             Image no 19.

In any case, reliable operation of the CHP unit is important in terms of ensuring the continuity of supply of heat and electricity especially when supplying individual/municipal clients. Another aspect in which reliable operation of the CHP unit is essential is to minimise losses related to providing emergency power to clients during the shutdown of the unit, and with prolonged shutdowns, the cost of ordered and unclaimed gas fuel and other penalties may be involved. Particularly high gas fuel costs occur at agricultural biogas plants, where it is impossible to “shut down bacteria” in the biogas production process while the unit is shut down. During the period of ongoing maintenance, overhaul or repair work, it is still necessary to carry out scheduled feeding of bacteria, so that the amount of biogas needed for the startup and operation of the CHP unit is sufficient. When a cogeneration unit in a biogas plant shuts down, it is common practice to burn the biogas on a “candle”. Needless to say, the biogas plant does not derive any benefits from the unproductive combustion of biogas. Therefore, to optimise the operation of gas CHP units and increase their uptime and availability, we have introduced a Stand-By service for our clients. It involves providing access to a mobile service technician within our country 7 days a week. The option of the arrival of a service technician from Eneria Ltd. provides many benefits to our clients. These include:

• permanent access to maintenance service,
• rapid verification of the defect,
• possibility of repairing/starting the generator during the arrival of a mechanic,
• in the case of more serious failures, the possibility of selecting the necessary parts to be taken away by mechanics assigned to fix the failure.

I hereby encourage you to learn more about our offer and contact us to discuss issues not addressed in this article. As an authorised representative of Caterpillar, we provide all engines manufactured by Caterpillar and MWM with a full service including:

• replacement of engine oil and engine oil filters, disposal of used engine oil,
• replacement of glycols in engine and mixture cooling systems, disposal of used glycol,
• performing scheduled maintenance,
• coordinating the work of subcontractors to service/maintain turbochargers, heat exchangers, dynamo, etc.,
• performing major and intermediate repairs,
• telephone and on-site consultations related to the operation of CHP units,
• sales of spare parts,
• wide-ranging technical support.

Feel free to contact us and benefit from our offer because properly planned and conducted service provides users with the longest runtime of gas-fired CHP units. Our mechanics, after performing all scheduled maintenance, are always ready to help our clients in all weather conditions.

 

mail: promanski@eneria.pl

Written by: Piotr ROMAŃSKI

CAT Industrial Engines Service Expert