Backup power is ever important today to keep plants running, businesses humming along and institutions like hospitals operating during power outages and disasters. Application designers can take a fresh look at standby gas generator sets when they consider systems designed for lean-burn fuels in emergency and standby applications. Lean-burn technology uses a high air to fuel ratio and excess oxygen to gain overall output efficiency at greatly reduced NOx emissions.
Why lean-burn for standby? While backup generator sets have traditionally been diesel and in some cases stoichiometric (rich burn) natural gas or propane, lean-burn gas gensets for use in standby applications delivers reliable performance, high fuel efficiency and very low emissions. So it’s no surprise that at Cummins Power Generation, we’ve seen increased interest in using gensets fueled by natural gas or even renewable gaseous fuels.
Another advantage of operating on natural gas is the ability to economically operate for longer periods of time for peaking as well as standby because natural gas is less expensive than diesel fuel for the same fuel energy content.
There are significant advantages of lean burn gas generator sets, but also some issues that you must be careful of. This does not mean lean burn gensets can’t be used for standby applications, but that there are considerations not required for diesel fueled generator sets.
Code Requirements. . There are unique starting and performance requirements to consider before putting lean-burn gen sets that run on natural gas (LBNG) into operation for standby, as opposed to peak shaving or prime power applications. First of all, emergency codes such as the NFPA 110 Standard for Emergency and Standby Power Systems and CSA 282 Emergency Electrical Power Supply for Buildings have requirements for quick starts, including 10 seconds for defined Emergency and some legally-required systems. Other defined systems may allow for longer times to start and prepare for load acceptance, while in other cases, no time provisions are specified.Equipment startup and load pickup capabilities are central to successfully applying a LBNG generator set. The design trade-offs for LBNG gensets can cause limitations in start time capability that are critical to some businesses and facilities. When don’t you want to go with a LBNG genset for your standby power? Especially in cases for loads that legally require generator set backup and require a fast startup in the 10 second range, it’s advisable to go with a diesel genset. Anything that can tolerate a longer interruption in power can be backed up by an LBNG genset.
Load pickup capability – To obtain the high efficiency and low emissions load pickup capability is compromised on a lean burn gas genset. Depending upon the specific model of generator set, the load pickup capability of a lean burn gas generator set can range from 10 to 75% of rated power.
Because lean burn gas generator sets are designed for continuous duty and very long life, there are some accessory items that are required including special oils, a way to power the pre-lube system when the utility has failed, and susceptibility to lower ambient temperatures.
If you’d like more information, please click here to download our White Paper on running lean-burn gas generator sets in standby by Tim Loehlein, Technical Specialist-Electrical at Cummins Power Generation.