Commercial Stirling Engines

Please revise this post for a number of spellings. It should be "Stirling" engine. If it works at temperatures below 110°, it will be quite inefficient, simply on Carnot cycle reasons.

Thanks for the spelling advice; it is too late to edit the original massage, so here it is:

I am looking for a >5kW commercially available stirling engine.

Preferably one that works at temperatures bellow 110degC.

Will appreciate any advice/lead.

I know it is not the best efficiency but that is power source that i have and need to produce electricity out of it.

Do you want a Stirling engine for a specific reason? I don't know of a market in Stirling engines. The Stirling cycle is a theoretical cycle which can only be approached, not duplicated in reality, because of the need for isothermal heat transfer. The use of the name may be misleading in an actual engine. The history of the Diesel vs. the Otto cycle in engine development (note especially the work of Diesel himself) and the history of how the current engines of these types actually work (which is far different from the theoretical) suggests that you should select your power conversion engine for it's actual performance, not it's name. When you don't capitalize the name of the designer/engine, your seem to be seeking a generic version (as otto vs. Otto) which will not have the efficiency of the Stirling cycle in any case.

As your heat source is low temperature, relatively speaking, the actual nature of it is important. Gas, liquid, solid? Air. water, rock? Waste heat? There is research and working engines using the temperature range you suggest, but if you are seeking a commercial engine, a real number is better, like "the temperature of my heat source varies between 106degC and 109degC, and my heat sink temperature is outside air temperature in Phoenix. Arizona." The use for the power is another variable. Some uses have different needs than others. Powering the electric lights of a hidden marijuana farm would prefer a constant, steady output, but pumping water to a parched community in a drought could use intermittent, variable load. Asking the right questions of yourself is the best starting point, then giving it to us out here.

You are right when we look into the details.

What i am looking for is any device that can convert waste heat that comes out of a chimney at an average 100 degC to electricity. I can convert the heated gas to heated liquid. Heat sink will be environment that ranges between 30degC in summer to 5degC in winter - average.

The quantity of the wasted heat is relatively large: 400kW when considering 20deg differential on the cycle.

The issue is that the temperature is too low for steam or micro turbines.

Again, will appreciate any advice.

I currently work for a Stirling engine company and there is a market for Stirling engines, there are a number of companies actively working in this field. The engines we are involved with are around 1kW so not relevant for this role.

To use 100 degC heat is very difficult. The efficiency of the engine is related to the ratio between the hot source and the cold sink. No-one would build a commercial unit to work at this temperature for efficiency and market size reasons, but don't let that stop you making your own. Demonstration engines are available that run off the heat from a cup of coffee, but the output is virtually nil. You could scale that up but I would expect the machine to be quite large but with the low temperatures the compoenents could be made from really cheap materials. Many Stirling engines are used for very cold cryocoolers (Philips) and have used cotton for the regenerators. Many components for such an engine could be made of plastic even.

Check out these guys: http://www.stirlingenergy.com/

I think they are geared more toward solar concentrators as the heat source, but in any event they are commercializing Stirling engines.

Thanks for the link.

I already checked them, they are too "hot" for me ~700degC is required for their generator and they are focusing on their solar system at the moment.

This site might be useful; lots of other interesting stuff on it too: http://www.redrok.com/engine.htm

The Stirling section is a long scroll down.

It might pay to drop a PM to Stirling Stan on the CR4 forum. I am sure he would be able to give you some experience info and avoid some traps in re-inventing the wheel.

http://cr4.globalspec.com/member?u=3179

http://www.stirlingengine.com/

Because of the modest temperature differences here, the engine will need to be relatively large. However, the pressure and temperature conditions will be mild. Maybe some scheme of bladders/bellows rather than pistons/cylinders could work. I don't have enough time right now to research this, but something promising might turn up.

You might also consider other ways to utilize the waste heat

The 100 deg C temp being mentioned makes it difficult and very-very expensive heat to utilize.

[Absorption Refrigeration]

there tend to be incentives for reducing peak electrical load, especially for commercial users

Just shooting from the hip as the OP hasn't really told us much about the facility, in any sort of food processing reducing the cost of wash water would be low hanging fruit, depending on the local cost of natural gas[or what ever fuel]

making electricity for waste heat tends to be rather pricey, There may be other ways to skin that cat [not Del of course]:D

Thank you all for the comments, if it will help bringing out some more ideas - here are some details about the facility:

It is a food related factory that uses several ovens that produce the heat, the reason why look for ways to utilize this heat is continuing raise in gas cost.

There is limited need for cooling and we already checked the absorption chillers which make a good solution with reasonable ROI (4~5 years), but this will use about 1/3 of the heat.

There is no need for hot water in the process or pre-heating for steam so this option is irrelevant.

There is a great demand for electricity so any savings there are welcome and that is the reason we look for waste heat powered electrical generators (Stirling or any).

...like preheat the incoming feedwater to a boiler, for example.

I have looked at some commercial Stirling engine sites to relieve my ignorance in this field and it appears to me that the name "Stirling" is used for closed cycle external combustion non-reacting gas engines regardless of the exact manner of heat flow. Is this true? The work I have been up to uses other cycles which are adaptable to using a variable temperature source and variable heat flow rate, what I call waste heat. If the heat volume is in a narrow range,as it seems to be in this case, that reduces the cost, which is my current concern. The Battelle Institute back around the 70's did work with Rankine cycle chlorofluorocarbon turbines at your temperature range. I don't know of commercial results. Size is the big elephant in the room in this situation. Handling large amounts of air efficiently without significant heat loss or degradation (damage, corrosion, etc.) can be expensive, so details of space and shape become important. My work is aimed at marginal economic situations, so commercial devices need to be at the developed level to be usable, and I didn't find any so far. I am following your situation with interest, but alas not much help.

http://www.tegpower.com/

Here is another place to look. These are peltier generators that use waste heat for direct generation of electricity. There are other companies that also use this method so don't stop with this one source.

Thanks for the lead. I am familiar with this method but never thought of it as a solution. I just mailed them an inquiry.

Don't believe it. Why would one hang around on CR4 waiting just-in-case, when a Google search will bring up all the answers in a few keystrokes (rhetorical question - NNTR)?