Hi,

I am assessing the potential of some geothermal resources and am unsure why certain people select binary organic Rankin cycles (ORC) whilst others with similar field properties go for binary steam cycles. I understand the flow and temperature of the brine has an impact along with the overall capital costs but what other technical factors determine the selection of the cycle type.

I would just really like to look at the field and brine conditions and be able to know if it will be ORC or a steam cycle

Any help appreciated

From  my limited experience it looks like the steam cycle units are on hotter or larger capacity sites.
You could look through the listings from the GRC ans see if you find any correlation.
I have seen a couple of installations that use a binary organic (butane) to drive a rotary screw expander in stead of a turbine.  These  look very reliable and have a wider operating envelope.  They are based on screw compressor knowledge.  They inject a little oil into the butane to seal and lube the screws.

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Plymouth Tube

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This website contains a good explanation of the ORC.

http://en.wikipedia.org/wiki/Organic_Rankine_Cycle

Reading between the lines, a bit, my understanding is that the fundamental advantage of an ORC application lies in tha ability to utilize a low-temperature source of heat AND the ability to save capital expenses through a low-pressure cycle design.

Steam cycles, as we all know, transmit heat and energy well but only at a (relatively) high pressure. High pressures translate into thicker piping walls, heavier and more expensive turbines etc...

Since waste heat boilers are a reasonable analog for proposed geothermal plants.....and since these plants only seem to make sense for power generation at 450F-500F and up, I would expect that any continuous steam source below about 450-500F would be a better candidate for an ORC.

My opinion only

-MJC
 

   

While binary plant is better suited to low tempeture fuilds, I have worked on projects where binary has been installed on quite high tempeture resouces, Some on these plants use a steam trubine and binary plant in place of a condenser and cooling tower. Others just have a binary plant.

While a condensing steam turbine will generate more energy from the same steam (MW/t/h steam)the binary plant has been used becuase of lower capital cost $/MW.