Natural Gas Versus Diesel Engines

As you had mentioned that the site is a remote location, obviously the logistics of moving the diesel fuel will be an expensive proposition. Further, building the storage tanks add to space and cost increases. Besides, the piping and the environmental issues regarding emissions have to be taken care of. As the HP of the engine is quite large, the emissions will also be high as the specific consumption of diesle fuel is high for large HP engines. I would recommend a Natural Gas Engine for use at this loctaion as you have natural gas readilyavailable. I prsume it is a well site producing natural gas. If such is the case, before selecting the gas engine you need to study and ascertain the flow rate of gas on a continuous basis, well head pressure, mositure content and the gas composition. Moisture and gas composition are important factors as presence of mercury, hydrogen sulfide and other impurities will impact the performance of the engines besides creating considerable risk to humans and equipment. The flow rates on a continuous basis must be known to esnure that you have suffcient gas flow to feed the engine. The well head pressure is important as the feed to the engine must be at a pressure else the gas may needs help of draught feed. Apart from that, the calorific value of the gas must be established to ensure that the engine will power up efficiently. The power rating is quite high at 2200 HP and there are only a handful of manufacturers who are manufacturing such gas engines and Caterpillar is the most reliable and established manufacturer of natural gas engines and I would suggest that you contact the nearest Cat dealer.I hope that this gives you basic info. to start with and the more info. you have on the gas produced, the better it is to select the engine and besides the choice is limited in the natural gas engines having high HP and thus your search narrows down to 3 or 4 major manufacturers

Great input from raotr (840). Just what I was looking for. You are right, it is a natural gas compressor station. Thanks again.

Years ago, I worked for the Enterprise Engine Division of DeLaval Turbine. The plant was (and still may be), in Oakland, California. They were designing and building "compressor stations" that were designed to run unattended in the natural gas fields around Rio Vista, CA. The engines were tri-fuel, v-16 of something greater than 2200 hp. These monsters were equipped with overhead cams, 4 valve heads, huge Brown-Boveri turbos. They were works of art and to c them run was a thrill. They were designed to run on diesel, natural gas and "swamp" or sewer gas (methane?). So, it's been done b4.

Many thks. Let me know if I can be of further assistance.

Diesel may be a better choice for a piston engine. Natural gas is rarely used (for emergency generators, for instance) beyond about 200 or 300 horsepower. The reason is that natural gas engines use engine blocks that were designed for gasoline or diesel. Above about 300 horsepower, most production engines are diesel, with high compression ratios and cylinder pressures, and robust construction. When they are converted to natural gas, the compression ratio must be reduced, and they must be de-rated. The result is that a 2,000 HP natural gas engine will be much larger and more expensive than a comparable diesel. If you want to use natural gas, try looking at a gas turbine. That is what is usd for compressor booster stations on gas pipelines.

The companies CH4 and Enertrade will know current information about this application. Coal bed methane is becoming a large field in Australia. There is a relatively new project at Moranbah West of Mackay in the Queensland coalfields that compresses coal bed methane and pipes it to Townsville where at least part of it is used for a power station. They have gas powered compressors. There is a similar project further south at Moura where the gas is pumped into the Roma to Gladstone gas pipeline and also used to manufacture ammonium nitrate. The large LNG plant at the Burrup Peninsular near Karratha in WA also use the natural gas to power the compressors. I'm still racking my brain for the details of a company which markets package gas power plants, which harvest their own gas. It is definitely available technology. If I remember I'll make another post.

Natural gas to power air compressors,is well known and established phenomenon.It is preferred option. In the present case,if plant design permits,it is preferable to use two compressors of lower capacity, instead of one large unit,from reliability and availability considerations of natural gas. Also there may be more manufacturers who offer gas engines at lower capacities.

I am not quite clear as how gas 'turbines' are preferred to gas 'engines'.Little more explanation will surely help.

Large gas turbines are generally preferred to gas reciprocating engines because they are much less expensive, have very few moving parts, and require less maintenance. They are not necessarily more fuel efficient. As far as I am aware, they are almost universally used for gas-fired pipeline compressors and for power generation. And the compressors are almost all centrifugal, for the same reasons.

The application in this case is quite different. The need is for an engine suitable to the local conditions. There is abundent availability of gas. Logistics for moving diesel is difficult and expensive. Besides there is no tankage available and needs to be built. Under the circumstances, it is advisabel to use the resource available locally and plan the equipment around the available means. Large gas engines are definitely available and Caterpillar manufactures gas engines from 55 to 4700 BHP ratings. These are nornmally V-12 engines with 10:1 compression ration and suitable for low quality field gas. I am sure that there are other manufatcturers who make gas engines and I am not sure about the maximum power ratings available from the others. But definitely the gas engines have evolved and commercial systems are available now and may be a reasonable alternative for the application mentioned.

There are other manufactures who supply Gas Engine. For instance we are using Rolls-Royce (formerly Ultein Bergen-Norway) make KVGS-16G gas engine for power generation. the capacity is 2.25 MW. It is a V-16 lean burn gas engine. The range of RR engines is from 2100 KW to 3600 KW & these are 12,16 & 18 cylinder engines. Please visit www.rolls-royce.com

geda.satish@yahoo.co.in

We have installed absorption chillers of 300 ton each capacity and presently operating on diesel but as the prices of natural gas are low i want to prepare a comparitive fuel consumption report.Can you help me in preparing the report?

Mr Rator has already provided suffient details as to how to proceed.No further discussion seems necessary. Can design permit use of 2 compressors of lower capacity, instead of one large unit,so that there are more manufacturers(of Gas engines)to choose from?

Can this be replied?

Yes, it is very much possible to design for two smaller capacity engines instead of one. However, it is a good industrial practise to have a back up in case one of the engines are down for any reasons. In such an event you will have to look one plus one back system, your economics permitting.

Presently planned is a sigle unit system without any backup. As rightly advised by you, it It is therefore recommended to have additional unit for backup,if economics permit. However,economiocs considers the cost of not having standby,i.e.loss due to resultant production loss,or decrease in profit,during outage of compressor.

You are very correct. Economics encompasses, the loss of production in case of shut downs due to equipment failure.The capital cost of equipment is miniscule when compared to the overall economics and generally, cost of equipment and operating cost would work out less than 0.1% of the over all costing of the operations. Hence, it is better to have a back up system rather than risk losing production

Glad that this discussion was very fruitful since an optimum solution to the problem could be arrived at. Contribution from Mr Rator was very valuable. Views from other participants,if any, may please be supplemented. Originator of this query may please let us know his feedback and proposed action.