Steam turbines work by converting the energy of high pressure steam into mechanical energy to turn an electrical generator or other piece of equipment. Steam turbines are generally designed for superheated steam applications. Now however there is new technology specifically designed for saturated steam.
The basis for this new technology is a screw compressor in reverse. Many will be familiar with a screw compressor, two screws turn and effectively compress the medium between them. The screw expander works in reverse, exhausting lower pressure steam out of it. The screw expander emerged from research work carried out at City University in London in the 1990’s. This work has been further developed into a working unit which is now available to buy in the marketplace by Heliex Power Limited. The expanding rotor design required considerable research so there is close to pure rolling contact between the moving rotors. The process fluid going through the machine effectively lubricates the moving parts.
It is typical for steam to be generated at a higher pressure and for it to be used at a lower pressure. Therefore the pressure of the steam is reduced near the point of use by using a pressure reducing valve, or now potentially with a screw expander in parallel, normally taking all of the steam load.
The reason for generating at high pressure and using at a lower pressure can be summarised below:
Potentially the screw expander can be installed in parallel with the pressure reducing valve station and used to generate electrical power. The screw expander is used to turn the electrical generator. Thought must be given to the use of power, preferably locally on the same site as the steam system. Even if power is not going to be fed back into the national grid a G59 panel and consultation with the local power company is required (UK customers). This is a similar to the steps required if power is generated through small solar or wind projects. By generating power in this way C02 financial savings can result. Heliex power are claiming payback in the region of 3 years for suitable applications.
Other potential uses include waste heat applications where steam can be generated which can then be put through the screw expander.
We look forward to following this interesting technology.
Posted by Admin on 07/09/2014