CNG Compressor Los Angeles Area: Packages used to refuel CNG transit bus fleet, significant energy savings over electric driven systems

Diesel Progress North American Edition, Nov, 2001 by Debbie Low

Don Lambert of Miratech Corp. added, "This system's air/fuel ratio controller uses the adaptive valve learn capabilities to track load and speed changes. This upgrade improves the response time significantly by permitting the controller to "map" valve positions with respect to engine load and speed. An improved response time means the controller restores emission compliance faster after a load/speed change. Keeping emissions from "spiking" during these changes is critical for a successful compliance test."

One of the most trying challenges for both the packager and station operator is how to maintain full load on the engine to optimize the catalyst and air/fuel ratio control equipment for the required three half-hour test periods during the fueling process.

Typically, the compressor package will start and stop three or four times during the eight-hour fueling process, causing the compressor to cycle through a cool-down period then through a warm-up period before going to full load. If a compressor is not at full load and the storage has not been replenished, fueling times begin to increase.

The key to making the project work was to smooth out the load swings caused by sporadic bus fueling. Trillium USA and J-W Operating worked jointly to coordinate changes both at the site and at J-W's fabrication facility in Longview to control the load on the Caterpillar engine.

"We were able to design a system that keeps the load relatively constant regardless of the amount of gas required by the buses." Poorman said. "This system also reduced the wear and tear on the machinery and simplified the control logic.

"Once tuned, the system allows the compressors to run for hours with only minor load changes regardless of the number of busses that are fueled. These minor load changes are quickly compensated for by the Miratech adaptive logic."

Barton said, "We have continually made changes at each division to improve fill times and decrease maintenance costs. So far we have been successful at each new site by standardizing in every area we can to reduce our spares inventory and maintain quality control.

"Our newest addition has been to go to an Allen Bradley PLC system supplied by FWMurphy to orchestrate the system between compressors, dispensing, and valving. We have also added additional displays at the fueling lanes that coordinate with the control room for continual monitoring of all components during fueling."

The new PLC design also allows for an additional fourth compressor to be added in the future if necessary Trillium is also working jointly with FWMurphy in the programming of the system to meet Trillium specific demands and requirements. Trillium uses callouts through a paging system and can restart the units from its Salt Lake City headquarters via modem when a shutdown occurs.

Jan Hull, Trillium president and CEO said, "2002 is going to be very exciting year for us. We will be installing over 2000 hp at a transit facility in New York in the last quarter of this year and are in discussions to add infrastructures similar to the LACMTA system. Our reputation and success in Los Angeles has really been our best advertisement and we are getting calls more frequently to take over existing sites as well as new transit installations."