Organic Rankine Cycle Plant

In 2012 Advance Boiler Services NZ Ltd (ABS) started investigating the option available to our clients to reduce their overhead costs. Mainly the energy costs. As a boiler supplier and heat exchanger manufacturer we had the skills to achieve this but lacked the expert knowledge of ORC plants.

Our senior engineer went to the United States of America on a renewable energy business mission which was organised by the Heavy Engineering Research Association of New Zealand (HERA). This trip was valuable in understanding the principles of Organic Rankine Cycle power plants and capacities required to produce energy from waste heat mediums.
We agreed to fund the supply of an ORC plant to be used on a 1MW Methane powered gas engine/generator. HERA had secured funding from MBE to help academics from various Universities in New Zealand to design and develop the systems required to operate an ORC plant. We were also fortunate to secure funding from Callaghan’s to deliver an ORC plant for trials using a gas engine waste heat.

We looked at, as most people do, a system comprising of R245fa refrigerant and a small turbine. The problem we would face would be that the refrigerant didn’t work with the exhaust temperatures developed in the engine and also there was minimal output heat load from this exhaust. By using a secondary heat exchanger, a reduction in temperature would be possible ensuring the refrigerant could operate in its specific design range without breaking down. The second problem being the output heat load, when using just the exhaust gases the energy output would not make the system financially practical. Using the engine head cooling water, the heat load could be increased to develop sufficient output to make the design viable.
Still uneasy on the turbine and availability of a suitable option, our engineer travelled to the UK to view a three stage turbine that had been offered to us. The turbine had been tested on Hexane, but there was no data to confirm it’s compatibility with the R245fa refrigerant or its efficiency capabilities. With the Universities theoretical and somewhat manipulated figures to make the idealistic designs feasible, we chose to work away from the data being supplied including the use of this turbine.
Months went by and we still couldn’t find a suitable turbine (with most manufacturers stipulated the heat load was too small, making the payback period too lengthy).

Finally, we came across a couple of companies that were making ORC plants using screw expanders instead of a turbine.
Not only did the supplier have an ORC plant operating on R245fa but also they manufactured an expander for steam. We are now keen to see where we can improve our client’s energy costs and also develop markets that we didn’t originally think about. Of course there is the increased output from the gas engines for the municipal waste, but now we have steam expanders for pressure reducing systems and the jewel in the crown geothermal plants using steam and hot brine water in low enthalpy wells.
Our company also spends time in the Pacific Islands servicing boilers and over the years we have come to appreciate the natural beauty of the islands. Unfortunately it is sad to see so many individuals limited in their person development simply because they do not have what we consider one of the basic needs, such as electricity. These island are forced to spend considerable amounts of the government funds on fossil fuel machines to provide electricity to only a portion of their nation’s people. I applaud the Pacific islands for the goals to maximise renewable energy and reduce the use of fossil fuels.
Even though the ORC units fitted to a diesel generator would not diminish the use of fossil fuels (until alternative fuels are developed) we can at least reduce the cost of producing the electricity by increasing the output without increasing the fuel. The pacific region has some fantastic manufacturing businesses that can use ORC potential energy diversification. The Pacific islands also are part of the ring of fire, which could provide electricity to their main grids and also remote supply where geothermal waste heat is available.

The screw expander design is not new, there have been screw compressors around for decades. There have been some manufacturers of screw compressors attempt to use their air compressor design to develop an ORC plant, but they have had limited success. Our supplier has developed a screw expander specifically for power generation, and not only have they field tested it but there are numerous plants around the world producing electricity at efficient rates higher than turbine designs. There is a geothermal plant in Mexico and now Indonesia is providing the opportunity for the steam expander to prove its worth.