The Ultimate Flexible Design
GEC was constructed on a 4.2-acre site adjacent to MWE’s Knoll substation, an appropriate location to plug in a peaking plant to supply electricity to central Kansas. Each of the nine gas engines is capable of supplying 25% of rated power within 2 minutes of receiving a start signal and can reach full power in only 10 minutes.
The engine’s part-load efficiency and low overall heat rate rival those of a modern combustion turbine combined-cycle plant, and the multiple-unit configuration gives load dispatchers much more operating flexibility than a combined-cycle plant for meeting system demand.
The key is the engine’s flat part-load efficiency curve (Figure 2). There are no wrong answers when dispatching these units — it doesn’t matter if the dispatcher brings two engines up to rated load one at a time or starts two or more units and brings them up to rated load in load-sharing mode. Don’t try that with combustion turbines, as dispatchers are obliged to manage a combined cycle as a complete load block. Another plus: Gas engine performance is not reduced with higher ambient temperatures or increased elevation, as is the case with a combustion turbine.
2. Even efficiency. The dispatch plan for the first five of the nine Wärtsilä 20V34SG engines at the Goodman Energy Center shows that very little efficiency is lost with part-load operation. Source: Wärtsilä
There is another important economic advantage to building a plant with multiple engines: Part-load operation results in little loss of efficiency, unlike operating a combustion turbine. This advantage gives an operator the ability to imbed into the dispatch plan a spinning reserve capacity. If the operator elects to operate all nine units at 90% load, then the plant has approximately 7.6 MW of spinning reserve that can be added to the grid in seconds (Figure 3). There are also tangible operation and maintenance (O&M) advantages with a multi-engine plant. With one engine out of service for an overhaul or service at GEC, only 11% of the plant’s rated power is unavailable. A combined-cycle plant lacks that level of redundancy or operating flexibility.
3. Big engine hall. The engine hall is split into two sections with six 8.4-MW, 20- cylinder engines on one side (pictured) and three on the other. Space has been allocated so that an additional three engines can be easily added in the future, as MWE’s needs expand. Notice that the front wall (right) is positioned to allow a crankshaft to be pulled after removal of the generator. Each engine generator system weighs 151 tons and is not bolted to the floor. Instead, each system is mounted on 20 spring packs that eliminate transferring engine vibration to the building foundation. Each engine holds 1,378 gallons of lubricating oil. Courtesy: Burns & McDonnell
GEC’s design also allows additional units to be added at a later date. Wärtsilä calls it adding units in a "rational" manner; incremental units can be easily added to the plant as demand for power increases, without affecting existing operations.
One more advantage of a multi-engine operation with fast-starting and spinning reserve capability is its ability to quickly provide backup to a grid supplied by stochastic generators, such as wind turbines with low capacity factors (<30%).
The facility requires few O&M technicians: Seven new full-time employees were added to four current employees of MWE to operate and maintain the plant.
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