Excerpt from Diesel & Gas Turbine Worldwide in their October 2014 publication.
Continuous duty gen-sets provide base-load power generation in diverse applications around the globe. However, high fuel costs and engine maintenance are pain points felt by operators. A low-maintenance path to significant fuel savings and lower emissions is what the U.S. Department of Defense (DOD) had in mind when they approached ElectraTherm to integrate the company’s Green Machine waste heat to power (WHP) generator with a 1.1 MW Cummins KTA-50 generator.
ElectraTherm’s Green Machine generator operates using a closed-loop ORC, where hot water is the fuel. Hot water from the engine enters a heat exchanger to excite (pressurize) the nonflammable, nontoxic working fluid, driving the twin-screw expander and generator to create electricity. The company said its twin-screw expander is unique in its configuration, lubrication and specifications, but the core technology is based on decades of proven compressor technology. The twin-screw expander has a rotational speed of 1800 to 4900 r/min, considerably less than turboexpanders, according to ElectraTherm. Unlike high-speed turboexpanders, screw expanders are robust units that tolerate “wet” dual-phase flow.
“This allows a very robust and cost-effective design for the Green Machine that can tolerate perturbations in both temperature and flow with turn down ratios of 6:1 available on demand,” said John Fox, CEO of ElectraTherm, Inc. “This is particularly advantageous in low temperature waste heat streams such as engine jacket water. Our Green Machine design is simplified and eliminates lubrication reservoirs, oil coolers, pumps and land filters, creating a simple, robust and efficient system with fewer parasitic loads and maintenance requirements.”
The Green Machine acts as the engine’s radiator, so the engine-driven radiator fans can actually be disconnected (or eliminated completely for a new installation), allowing more work to be performed by the engine to generate additional electricity. In effect, the engine’s waste heat becomes a source of cost savings by displacing the radiator’s capital cost and parasitic load.
Between the DOD project and the machines currently running in the field, ElectraTherm said it increases fuel efficiency up to 12%, depending on engine size and configuration, and site conditions while featuring simple installation, mobility and low maintenance.
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