What are some technical problems with generating electricity using a gas turbine or combustible engine at a gas flaring site?

Question

Numerous oil and gas exploration sites practice flaring for safety and disposal of unwanted low calorific gases. However, instead of just standalone burning the gas, why can't a gas turbine or internal combustion engine be attached so that the process also generates electricity. A lot of heat is being wasted. Why not convert to power?

I'm guessing there are some technical or economic problems to this. Otherwise, it would have been long implemented. What are the specific issues?

Answer 1

I think this is a situation of "the devil is in the details', and of course, cost. In the US, gas from a few wells would not likely be of sufficient volume; but several/many wells could be combined (detail = pipeline plan and control). There are wells, mostly Middle East that do have enough flare gas. As a point of reference the last local power gas turbines I saw were Rolls RB 211; an engine family that powers wide body planes. I don't know how much gas the need but it must be substantial. (The RB 211 was at a gas plant fed by a hundred wells). Smaller engines could be used but with less efficiency (higher cost). Then you need power substations, power distribution lines (likely long) (more details). On the other hand, my employer also generated remote power with old used J 47 s(?) engines. Salvaged from older obsolete jets. It appears that a good answer would require research.

Answer 2

It is less economical to harness this energy/materials. From the perspective of the company, money is better spent on their immediate business needs such as locating large resources or improving the thermodynamic efficiency of their refinery.

Reasons it may be less economical include:

1. Intermittent flow; flow may be zero for long periods, with intermittent spikes or pressure reliefs. It is not economical to build a very large thermal generation system that is only heated occasionally. This is the same reason that hydro electric power plants have spillways that are often flowing water. This water energy is wasted, but it is not economical to build the hydro turbine capacity to handle large spring water flow rates that will only be utilized for 1 month of the year.
2. Gas composition; the flow may be filled with lots of non-combustibles that decrease efficiency (low calorific like you mentioned). The variable composition Can change flame temperature requiring exotic high temperature materials, even though most of the time it operates at low temperature. The composition may have corrosive materials again calling for exotic materials.
3. Regulations; it is extremely difficult to get a combustion based power production system permitted (at least in the United States). It is very likely that it is easier to permit a low temperature flare that wastes 100% of the stream, than it would be to design an permit a boiler/turbine that has to hit X ppm NOx and Y ppm CO standards with a constantly changing gas composition. Its counter intuitive, but the EPA is focused on discouraging all combustion (in favor of wind and solar), rather allowing companies to improve the efficiency and emissions of combustion.