BLOG: Power Perspectives

[#1]

Did you know that fuel is the single greatest factor affecting engine maintenance and operating costs? The reason is that the composition and quality of fuel affects the heat and other characteristics of combustion in the engine cylinders.

There are many sources of fuel that can be used in gas engines, including:

• pipeline natural gas
• wellhead
• bio-gas
• propane

 
It is important to know your fuel. For example, varying levels of Low Heat Value (LHV) and methane can put air/fuel ratios out of balance. Fuel impurities can degrade engine components. There are several factors that can impact operating performance and maintenance needs, some of which I've outlined below:

Maintaining Proper LHV
Each commercial fuel gas is a mixture of gases. Some of the gases are combustible and some of the gases are inert. The compositions of these gas mixtures have extreme variations. Routine testing of the fuel will help you determine that the proper Low Heat Value (LHV) content is being maintained. The LHV of the fuel can impact the engines overall performance:

• LHV that is too low can result in starving the engine for the fuel energy necessary to produce power.
• LHV that is too high may cause the fuel system to be unable to mix air and fuel in the proper ratios, resulting in poor combustion and reduced power.

 
Methane Content
A fuel's potential for detonation is indicated by a methane number and should be monitored. Methane is the major constituent of natural gas and is released during the decomposition of plant or other organic compounds.

Depending on the manufacturer, gas engines can operate successfully on a range of gaseous fuels. However, adjustments must be made to the fuel system when the fuel is changed to maintain proper air/fuel ratio in order to comply with the emission requirements for your site.

Contaminants & Filters
Contaminants in the fuel can also affect engine life. Gaseous fuels contain a number of contaminants that can attack different engine components and lead to early failure. Monitoring your fuel will help you avoid costly down time and possibly major failures.

Fuel filters are no less important than air filters to protect gas engines from dirt and debris. A proper fuel filter removes impurities that can damage the internal components of the engine. Proper treatment can remove the following:

• Moisture
• Particulate Matter (PM)
• Sulfur
• Siloxanes (partial removal only)

 
The gas must be supplied to the engine at a pressure that is acceptable. For optimum operation, use a fuel filter that is properly sized for the gas pressure. In fact, for many gas engines, fuel filters are a provision of the design for the application.

Questions
Do you regularly monitor you natural gas LHV and/or methane levels?
How do you reduce contaminants in fuel?
Are there any additional tips that you have on fuel not mentioned above?
Do you adjust your maintenance intervals based on oil/fuel sampling?

Please post your feedback below.

[#2]

gashaka,

You are right, fule is import for a gas genset project successful operation.

In China we have some landfill, coal mine methane project, you know in landfill gas and coal mine methane, there has 100% moisture and some PM, we use a systems called pre-treatment to remove these. pre-treatment unit with chiller can remove moisture to below 80%, which is acceptable for gas engine; and use primiary filter and fine filter to remove PM to 1um. also use blower to maintain the gas pressure.

H2S in landfill or biogas is harmful to gas engine parts contains copper. we ask third party use biochemial to remove H2S to Sulfur and remove it before inlet of gas engine.

Your article is good, hope can read more in future.

Thanks

wangzzy, China

[#3]

Treatment raises a good question.  At what point does the cost of treatment outweigh the cost of increased maintenance or downtime?  SIloxanes are increasingly becoming more troublesome in landfill gas, but treatment systems may start at $500,000 in capital, with additional $50,000 or more in O&M on the treatment system, per year.  Landfills are currently trying to find the point of increased engine O&M and lost availability, beyond which it makes economic sense to add treatment.  I would be interested in other's experience.

[#4]

Matt, You make a very good point as to what point does the cost of treatment outweigh the cost of increased maintenance. Because of site fuel variations there is no one right answer that fits every case. You should get a complete fuel analysis and then evaluate the different fuel treatment options and costs based on the analysis. Develop maintenance costs in $/kW-hr based on treated fuel and without treated fuel, compare and evaluate options. This way you can review the costs and benefits to fuel pre-treatment. It may be you can realize benefit using minimal fuel pre-treatment. The right answer for any one project could be a combination of treatment and optimized engine maintenance practices. Landfills today are a lot different then what we were used to 15 - 20 years ago. Good Luck

[#5]

I run four landfill sites and we don’t treat the gas as well as we should. Moisture in the gas is very important as we have found that acids are carried into the engine with the moisture. By reducing the moisture we have extended our oil change intervals from 400 hour to 875 hours. Kent makes some good points with gas quality; the problem we are incurring is the higher the Methane 40 % up level the lower hours we are achieving on our spark plugs. We have tried Cat, Champion and Bosch plugs and are only getting 1500 hours before replacement with one clean in between. We also have played with engine time to reduce burning of cylinder head valves and reducing cylinder head temperatures, we are achieving 10,000 hours. I would be interested in experiences of other landfill operators.

[#6]

Dave,

Sounds like you are on the right track. I too have managed

LFG sites (22 engines across 8 sites and 2 coasts). We found moisture too to be a big problem at all of the sites regardless of regional humidty levels. Because most sites have the engine placement at the base of the landfill there is an inherent problem with water intrusion and damage to the prefilter/chiller systems. Once that happens it is just a matter of time until the moisture gets in the engine.

With regard to burned heads (exhaust valves) there are several things that I have seen; low oxygen content (less than .5%) in the gas being the most prevalent. Also leaking valves due to contamination or bad rebuilds (wrong seat angles) have been a problem.

I have had to develop a customized maintenance program where we strictly depend on oil analysis, valve recession and compression levels. In addition we have tossed the old calendar day schedules and base all maintenance on engine hours. This seems to work the best so we get the most out of our downtime.

Because most of these sites are somewhat remote, vendor response can be delayed and as you know extended downtime is extended money loss.

If you would like to further discuss issues contact me at pervin12000@yahoo.com

[#7]

 After a year and a half of testing different run times with oil,filters and plugs we found what works for us is, At 1000 hrs ( give or take a few hundred ) we do plugs,oil,filters,valve set. (need it or not)

We found an oil that can go 1000 hrs before it starts flagging using good filters and 2 separate analysis programs ( to keep the oil supplier honest )

Plugs, we found that cleaning them did not benefit us well, too many miss fires,shutdowns etc. We now go with a "one and done theory" with a cheaper plug (champion)  They will just make 1000 hrs.

Valve set every 1000 hrs.

I'm at a 98+% run time with a $1200 maintenance cost per 6 weeks.

My point is, Spend the time and money in testing, In the long run it will pay off!!! 

[#8]

Hi

this cool! thank you so much for sharing your knowledge to us.. very well appreciated!

Air Filters in Wisconsin

Thanks again...

[#9]

The older landfills seem to produce more siloxanes since they began before trash recycling. The newer landfills are sealed better but still have a lot of waste dumped into them that cause siloxanes to attach to the gas. Drying the gas out makes a big difference in both reducing siloxanes and increasing power output.  On a low humidity day with low humidity in the gas supply stream, the exhaust temps run lower so more of the heat is used to make power rather than going up the exhaust stack as super heated water vapor. Humidity also takes up some room in the combustion chambers and piping which has no effect on producing power.

 Landfills are hot inside and oils and hydrocarbons evaporate just as a pan of mineral spirits would evaporate if left out in the sun on a warm day. These hydrocarbons and oils also pick up siloxanes just as the water does but are much harder to knock out as condensate. This is because they are much lighter than water. I once seen these hydrocarbons condensing in my headers and above ground landfill piping but only when the ambient temp was -20F. This occured one early morning but as soon as the day got a little warmer( around 0deg ), they completely disappered. The oil was very light in color and wieght and smelled like mineral spirits. Because these hydrocarbons are of a different molecular makeup than CH4 they also burn slower or faster than the primary methane fuel. They may require different amounts of oxygen in the combustion camber to burn correctly.

 I've found that if the gas quality is dropping in the header to the plant, the amount of siloxanes will also drop and if it is rizing the siloxanes will also rize in the gas stream. Dosen't mater if the gas quality is 40% or 60% although hotter gas seems to create more siloxane. The gas is always cleaner in the dry months of summer.  During the winter months there is a wider swing of  the barometer because of bigger changes in outside temps caused by strong fronts and storms. This causes the landfill to (exhale) during the storm or before the front passes. A cold front occurs right after the storm causing a dramatic increase in baro pressure which in turn causes the landfill to inhale which now weakens the gas with Oxygen and Nitrogen. My valves will usually burn right before the cold front comes thur. This is probably because the baro pressure is at its lowest point at this time and since the landfill is still exhaling, the gas is at its hottest state. Since no Oxygen has been getting into the landfill during its exhale, the landfill had a chance to start heating up again and putting more silicone into the gas stream. The barometer is measuring in inches of Mercury but we measure well vac in inches of water. One inche of Mercury= a lot of inches of water so you can see how much baro pressure changes things.

 I have also noticed that leaks in the capping and around wells affect how much siloxane gets into the gas stream. I think that a tightly sealed hill and the proper extraction well balancing is one of the best ways to lower siloxanes. If gas is not constantly pulled from all area's of the landfill, oils and siloxanes will saturate the gas stored in that area then move toward wells during storms and changes in baro pressure. Capping and well bore seal leaks prevent system vac from reaching out and pulling stagnent gas from area's father away from extraction wells. The oils, siloxanes and H2S rise to the top and if a hot well is opened after being clossed for awhile, the engines get a full shot of all this stuff in the saturated gas. Same occurs if the site is down for awhile and the gas is not being flared off before starting the engines.  

 After running a dirty gas landfill site for 20 years and changing more than 500 cylinder heads these are some of the things I've found to help a little. The best way is to install a good gas cleaning system because no mater what, the siloxanes will always cause valves to burn and other problems. Running lean will help just a little but there is no way to keep silicone from building on valve seats unless the gas is clean and dry. Every time a engine is taken off line to replace a head, the gas has a chance to rebound and bring in more silicone unless it is flared during that period. Also power failures that that the site down  during storms cause a even worse problem at the worst possible time when the gas is at it's most rapid increase in quality and silicone. 

[#10]

Is any one running an engine off of syn-gas from a gasifier?

I have tried to find information on the cat web site for engines that can run on this fuel so far it seems that the only supplier of engines that are cabable of running on the syn-gas are made in China

They range in size from 500KW - 1.2 MW / run 500 RPM and are claiming they can run an average of 20,000 hours before major maintance 

They have several instalations at rice mills that have been running in excess of 12 years with out major problems of tar build up in engines and are said to be reliable 

If any one has any knowledge of a gasifer system in the US that is producing clean syn-gas from rice hulls please let me know 

I have heard that some small turbines are able to run this fuel as well but have yet to find a manufacturer

I'm  looking to installing a 4 MW China Gasifier plant at our rice mill located in the Philippines but the only technology that seems to be available is from China  

Is anyone doing this in the USA

Thanks

[#11]

Hello Tom,

I'd be happy to share with you the different options that Caterpillar has available for generator sets operating on syngas fuel.  Will be in contact.

Nick

[#12]

i follows up more 20 Mwe of biogas digester in italy, we use MWM engine, becouse cat politica before MWm acquisition, i have syngas engine running and gassificator in my home lab running, soo i have only nore 25 years i enegy sectors,soo not natural gas use manutance cost is a lot if not to do this:

clean proply the gas before engine

not use small zise to save small money of pipe. mi esperience most eng not make good dimension

use good blower to push gas under invert

gas need cooled before engine under 15/20° celcius

we have try all different all time more cost and haeds a lot valve eccc..eccc.   ecc......, soo special if you have station with 4 engine in paralleling to network and customer want save money need patient to exsplain hem thecorect via to product energy is not same go to bar or pub,

we have a lot of landfill engine in operation but is 80% GE jeanbhacher 320, MWM 2020 tg serie, and some last Cat 3512 not more, the dealer  CGT inperson of  doct  A.Cernilia now he have start after new campain for cat engine istallation, MWM yellows next year maeby, but is to hard becouse after years without presents on mercant,

cost all competitor is more espensive of cat engine, and more difficultose to found spare parts, electronic problem becouse PLC use all is looked, by password also for change stupid parameters, esample carburation mix, becouse all days gas so be different, run from 48% of ch4 to 55%, without some adjust is not possible running proply, all full autority controll i have a lott of problem MWM incluse, the best is fuel controll by trim valve and lambda, we have lambda controll in syngas use engine, we want to try in biogas digester,

good carburation reduce cost and increse haeads and valve,

engine oilq,uality with support fron vendor is 50% less problem, we replace oil now at 4000 hours without problem, we take esample every 500 hours and we have feedbak in 24 hours, emd of storuy is cost reduction

soo basicle nothing new in Cat word but need push dealer to spend more money and time to do good relation ship and service the customer 24H, energy engine in not a tractor, need change mentality to many operators from Cat dealer, still old thing,

esemple is mi station in Alessandria, wen we have start project i have look for 4 3520, but dealer spook, cat not make warranty and efficensi is low of competitor, real esperience competitor is only more aggressive on merchant, efficenty is same but not more, all is carburation, learn burn engine cat is same but not less competitor, lambda 1 is more cost for exsaust system (3 VIA catalist), efficence is not cover the cost, soo better learn burn engine,

wat is need, sample engine (old Cat style), good service from local dealer, trainig customer for basic service use, not 100% only from service,

give to customer instrument , parts service manual ecc ecc...or via web tool to follows and make some service to engine, customer ias your font of business,

about syngas use all is invitate to see perkins modificate from me running with syngas, 80 kwe, in italy,local dealer next week make visit to me

maeby  i try to put some movie and picture

saluti a tutti regards Claudio Gordini  

 i do no if some body understam me (bad englice sure),