Dresser Waukesha has developed a new 1 MW-class gas engine for power generation through a US government programme to increase efficiencies and lower emissions from large gas engines. Here, Albertus Dijks shares the experience gained and lessons learned with the engine in its first few years of operation.
Cogeneration plant at an Italian factory for food packaging material. The exhaust gas heat exchanger is in red
Historically, Dresser Waukesha has served both the gas compression and the power generation and cogeneration markets with the same types of engines. Because the compression market demands reliability while the power generation market prizes efficiency, Waukesha engines have developed a reputation for reliability and good efficiency. However, good efficiency is no longer sufficient for today’s cogeneration market, which demands the highest possible efficiency ratings.
The 16V150LTD was designed as Dresser Waukesha’s answer to the demand for high-efficiency gas engines for the power generation and cogeneration market. It was developed through the ARES (Advanced Reciprocating Engine Systems) programme sponsored by the US Department of Energy. The ARES programme was created to accelerate the development of large natural gas engines that operate with increased efficiency – while meeting tight emissions requirements, maintaining current levels of reliability and durability, and reducing ownership costs. The resulting new 16V150LTD delivers a leap in efficiency and power density making it highly competitive in its class.
Since the engine was introduced in late 2005, more than 100 engines have been sold – all of which are driving generators and are being used in pure power generation installations and in various cogeneration systems. These include greenhouse installations, where maximum benefit is derived from the fuel consumed – by providing heat for the greenhouse and electricity which is used on-site or sold to the grid, and using the CO2 produced by the cogeneration process as a plant fertilizer. Many of these engines burn natural gas, but several are fuelled by biogases. Most engines are on the grid, while some operate in ‘island’ mode or in parallel with another engine.
Power Ventures installed a generator in an Italian factory for food packaging material, based on a 16V150LTD gas engine
Because they are operating in widely varying applications, under varying conditions and with varying requirements, the new 16V150LTD/APG1000 units have provided a wealth of field performance data.
Piping for process heating
The 16V150LTD has proven to be an adaptable engine that has performed successfully in a wide range of applications around the world. In regions where the electricity grid is at capacity or is not reliable, 16V150LTD-driven generator sets provide reliable, on-site power generation. In regions such as the US and Europe, where there is a greater emphasis on maximizing fuel efficiency, these units are operating in cogeneration installations, either on natural gas or on biogas.
A good example of cogeneration is the unit installed in an Italian factory for food packaging material. Previously, the plant used boilers to produce hot water and steam, and was buying electricity from the grid.
Our distributor in Italy, Power Ventures, installed a generator based on a 16V150LTD gas engine – as shown in the photographs. The electricity is used in the plant and the excess is delivered to the grid. The heat from the lube oil cooler, intercooler and jacket water is supplied to the hot water system, while steam is produced from the exhaust gas, (the dark red exhaust gas heat recovery steam boiler is also shown in the photos). The new system, which has been operating since autumn 2008, delivers significant fuel savings as compared to the conventional production of hot water, steam and electricity. One of the options that we are currently field-testing is high temperature jacket water-cooling. For applications that do not need much hot water, this can be used to produce low pressure steam.
Greenhouse applications for the engine generator unit
Another typical application is for greenhouses, especially as found in the Netherlands. The electricity generated in these installations is used either in the greenhouse or supplied to the grid. If the electricity is supplied to the grid, the engines run when the price of electricity is high. Depending on the contract, this can be either at normal peak hours or when the price at the exchange market is right. The heat from the engine may be used immediately or stored in huge water tanks for later use. In addition, most of these applications also use the CO2 from the exhaust (treated to remove NOx, CO and ethylene) as a fertilizer in the greenhouse.
SELECTIVE CATALYTIC REDUCTION
The 16V150LTD/APG1000 in a greenhouse with CO2 fertilization uses an SCR (selective catalytic reduction) system to remove CO, NOx and ethylene from the exhaust gases.
When the first 16V150LTD with SCR was commissioned, we determined that it was critical to establish correct engine settings at part-load operation to meet the requirements of the SCR system. The engine had been tested at the factory in Waukesha, Wisconsin, USA, with the pipeline quality gas as delivered in Waukesha, and then set for Dutch natural gas. The engine and SCR system worked well when the engine was operating at full load, resulting in relatively stable emission levels and exhaust temperatures.
At the first start of the engine we found the temperatures in the SCR were very high at idle and low-load operation. The engine had to be shut down to avoid destroying the catalyst material because the SCR was not equipped to bypass the high temperature exhaust gases. We shut down the engine and made necessary adjustments, after which the engine and the SCR performed effectively at all load levels.
Soon after the release of the 16V150LTD/APG1000 for natural gas, we introduced a biogas version. The use of gas from biomass or waste is becoming increasingly popular in Europe and other parts of the world. Our plan has been to offer the engine on a limited basis and conduct field testing prior to making the unit more widely available.
One of the first 16V150LTDs operating on biogas was commissioned in Belgium. This site uses part of the heat for the digester while the remaining heat is delivered to a nearby resort. Preliminary reports, which are subject to additional verification, indicate that the total efficiency and electric efficiency for this installation is very high.
Generators also operate in so-called ‘island’ or stand-alone installations. Stand-alone power sources are often found in mission-critical applications, such as hospitals, where continuous power is essential, and in regions where the grid is either unreliable or has insufficient capacity to meet market needs.
There are also situations in which it makes economic sense, such as in greenhouses in the Netherlands, where the operators rely on their own generators – set up for combined heat and power (CHP) – to supply their greenhouses with electricity, heat and fertilizer (CO2 derived from the engine’s exhaust).
In the Netherlands, we have an APG1000 running successfully in island mode in a greenhouse application which has demanding lighting requirements.
‘HEDERA’ EFFICIENCY CASE STUDY
As noted earlier, the 16V150LTD was developed specifically to be a high-efficiency engine, as part of the US Department of Energy’s ARES programme. The production models of the engine have an efficiency rating of 43.6% at TA-Luft (a German air control regulation) at specified operating conditions and fuel quality.
When an engine is specified for a particular customer installation, we issue a Special Application Approval which defines the engine’s performance parameters, including the efficiency for that installation. For cogeneration applications, we generally state the efficiency according to ISO 3046 which has tolerances of 0 and +5% fuel consumption. In practice, however, our customers often find that their engines use less fuel than noted in our specifications. One example is the ‘Hedera’ greenhouse in the Netherlands, where the efficiency of the 16V150LTD has been certified as ‘better than promised.’
The Hedera greenhouse operates two 16V150LTDs, which were among the first of these engines sold in the Netherlands. The engines were commissioned in the autumn of 2007 and have run well since.
A customer’s remark that the engine consumed less natural gas than expected, prompted Enerflex, our distributor for Benelux, Spain and Portugal, to have the efficiency of the engine verified by an independent testing organization. Enerflex engaged Bureau VERITAS to measure the efficiency and emissions of one of the engines in the Hedera installation, to establish a valid comparison between stated and actual performance of the engine.
Bureau VERITAS used well-defined protocols to sample the fuel, and certified instrumentation to measure fuel flow and the electric power production. When the engine had run for about 6000 hours, data were taken in three sets, of a half hour each, and averaged.
The ISO efficiency promised for the engine under site conditions and TA-Luft NOx emissions was 42.8%. The actual efficiencies, as measured by Bureau VERITAS, averaged 43.8% while the actual NOx emissions were 13% below TA-Luft. The 43.8% measurement assumed an electrical efficiency of 97.4% for the generator. Therefore, even though the NOx emissions were well below established limits, the engine was operating at a full 1% above the stated efficiency.
The CO and CxHy (hydrocarbon) emissions also were measured. They were found to be well below the specified levels and were low enough to meet the very demanding levels required for subsidies for the Dutch greenhouses. The low emission levels of unburned fuel help to achieve the engine’s high efficiency.
Endurance and field testing have proven that the new engine is operating well on targeted maintenance intervals. Historically, there has been very little feedback on maintenance experience when everything is running as expected. And in the case of the 16V150LTD, in order to find out what customers have to say, we had to ask:
Oil life and consumption
The service interval was defined as 1500 running hours on natural gas. Field tests and the information we have received from customers confirm that this is appropriate. Several oils, such as Citgo Pacemaker, Mobil Pegasus, and others, have been used successfully. Any oil found in the Dresser Waukesha oil recommendations sheet, which meet the specifications for the 16V150LTD engine, can be expected to offer similar performance. However it should be noted that oil analysis should always be used as a guideline for engine oil life and oil change intervals should only be modified based upon these analyses.
When the engine is running on landfill, digester or sewage gas, the oil life depends on the cleanliness of the fuel – which typically ranges from poor to very poor – as compared to natural gas.
We also evaluated total oil costs, as defined by the frequency of oil changes and the need for top-off oil to compensate for the engine’s oil consumption. Customer feedback on the 16V150LTD is that oil consumption is low. Numbers we found were around or below 0.1 g/kWh. This offers multiple benefits. It limits the exposure of SCR and exhaust gas heat exchanger to contamination by oil products carried in the exhaust gasses. Low oil consumption also helps keep the combustion chamber and the valves very clean.
Although current service intervals are being met, Dresser Waukesha is actively pursuing improvements in overhaul intervals. The intent is to maintain the low oil consumption but increase overhaul life, thereby reducing operating costs even further.
The target for life of the Waukesha spark plug was one service interval – from field testing and feedback of customers, this has been proven to be met.
On a new engine design, overhaul interval estimates can be difficult to define. To ensure good data, a large fleet of engines operating at maximum load for extended periods of time are the best indicator of meeting overhaul intervals. Because no 16V150LTD engine has reached the crankcase overhaul interval, Dresser Waukesha has combined data from numerous field test sites with lower operating hours and from high power endurance tests run in our own engineering lab to determine if overhaul levels are acceptable.
Both the physical review of used components, and analytical means, are used to determine if the promised overhaul levels will be met. Evidence supporting our projections is based on the wear condition of the main bearings after 13,000 running hours. In addition, we are looking at improvements which extend intervals on valve service.
As with the release of any new engine, early field experience has pointed to opportunities to make improvements, among them, some changes to wiring to improve durability and to simplify servicing. All in all, improvements identified during the introduction of the 16V150LTD/APG1000 have been relatively minor and have largely been addressed by educating the factory and the field on the unique characteristics of this engine.
The 16V150LTD engine, and the APG1000, its generator set counterpart, is a high-efficiency engine. Although this engine represents a large step in performance, compared to older products, and has required some different thinking, the introduction of the 16V150LTD has gone very smoothly, with only minor issues to be resolved.
Further refinements to the engine and generator set will only improve performance, operating costs and initial quality, making a good engine even better. As additional field tests are completed, the engine will be released for more and varied operating conditions, eventually allowing it to replace lower efficiency engines in most applications.
Albertus Dijks is with Dresser Waukesha, Appingedam, the Netherlands.
The author wishes to thank all those who contributed to this paper. Special thanks to Larry Wilson of Dresser Waukesha for the information and assistance provided.