Small automatic steam turbines, generating up to 275 kW of three-phase electricity from wasted energy in pressure-reducing valves (PRVs), have the potential to make small-scale electricity generation commercially viable.
Innovation company African Technical Innovations reports that the Microsteam turbine, created by US-based energy research and development firm Energent Corporation can generate electricity at a cost of between R0,25 and R0,28 a kWh using mostly energy that would have been wasted.
African Technical Innovations MD Kobus Engelbrecht says that many factories and industries have steam boilers using PRVs, operating at 8 bar to 10 bar. He notes that, while a PRV reduces the pressure, it also wastes energy.
“One could compare it to continuously pumping your car tyre to 10 bar and blowing it down to 1 bar. All the work that went into compressing the gas is reversed or lost in the pressure-reducing operation,” he explains.
Microsteam turbines make use of this lost energy by using the steam to spin a turbine and generate electricity. However, Engelbrecht notes that, because most boilers operate at saturated steam levels, and not superheated steam, mechanical and other losses necessitate the addition of a small amount of steam.
“Where a steam flow of 5 t/h is reduced from 10 bar to 1,5 bar by a PRV, the Microsteam turbine can generate 275 kW, but it needs an additional steam flow of 500 kg/h to accomplish this. Depending on the cost of steam, this translates into a cost of R0,25 to R0,28 for every kilowatt hour ,” he asserts.
A typical baseload power plant has a thermal-to-electric conversion efficiency of 40%. Engelbrecht says that the Microsteam turbine can achieve an overall system efficiency as high as 93%. This is accomplished because the Microsteam system uses the outlet steam as a heat source for dryers, desiccators and adsorption chillers, which is a very efficient use of the total energy in the system, while, at a power plant, all the energy is used to generate electricity.
The Microsteam turbine takes advantage of the fact that there is still an end-use for the steam and converts a small amount of the total energy in an efficient way. “If there is no end-use for the steam, the overall cycle efficiency drops significantly,” Engelbrecht notes.
The Microsteam unit fits through any standard 2,1-m door and is skid-mounted and fully automatic. Engelbrecht says that it can accumulate up to R37-million in electricity savings over the first 12 years and has a design life of 20 years. When the system is operational, it should reduce the maximum demand of the customer by 275 kW. At full capacity, each 275-kW Microsteam turbine has a carbon dioxide (CO2) reduction equivalent of 1 600 t of CO2 a year.
The company focuses on green alternative energy. Engelbrecht notes that South Africa currently faces significant electricity supply challenges, and there are two possible solutions.
“Building new power stations is one solution to the challenge, but people can also start generating their own power. Generating your own electricity on a small scale was seldom, if ever, commercially viable in the past, but it is now,” he adds.
African Technical Innovations will be making the Microsteam turbines available in South Africa soon.