POWER July 2017 - 28

ENVIRONMENTAL ISSUES
Humboldt Bay Generating Station:
A Case Study in Emissions Control
Troubleshooting
It can be a challenge to keep emissions in check while operating dual-fuel reciprocating
engine technology during low-load conditions. However, doing
so is especially important under California's strict emissions requirements.
The Humboldt Bay Generating Station team did just that by taking a critical
look at multiple emissions control systems and identifying several
process modifications that improved overall plant performance.
Silas Biggin, Chris Brittain, Chuck Holm, Jill Lorenc, and Scott Washington
H
umboldt Bay Generating Station
(HBGS) is a Pacific Gas and Electric
(PG&E) owned and operated facility
consisting of 10 Wärtsilä W18V50DF A
engines. The plant is situated on Humboldt
Bay in northern California. Each four-stroke
engine is capable of producing 16.7 MW
(gross) to provide a combined station net
output of 163 MW.
The 10 engines feed two 60-kV local
distribution lines and one 115-kV transmission
line. Bus-tie breakers located prior to
the step-up transformers allow reconfiguring
engines to other line resources, as necessary.
Each engine is capable of operating between
full load and the permit minimum load of 10
MW. The station entered commercial operations
in September 2010.
HBGS was constructed to replace an aging
gas-fired boiler facility residing on the
same property. Dual-fuel type reciprocating
engines (Figure 1) were chosen for three
main reasons: Humboldt County's relative
remoteness; lack of redundancy in the natural
gas supply; and the risk of natural gas
curtailment during cold weather. The engines
normally operate on natural gas with a small
amount of light fuel oil (LFO or diesel fuel).
However, during emergencies all engines are
capable of operating solely on LFO.
How It Works
Burning natural gas in a diesel-cycle engine
requires the use of either a spark plug
or small amount of LFO to ignite the natural
gas. Operating in dual-fuel mode, each
engine is required to utilize California Air
Resources Board-certified LFO as pilot fuel
to ignite the natural gas burned in the cylinder.
The natural gas enters the engine with
28
1. Reciprocating engines. Humboldt Bay Generating Station (HBGS) has 10 Wärtsilä
W18V50DF A dual-fuel type reciprocating engines. Courtesy: HBGS
the combustion air on the intake stroke, and
pilot fuel is injected just prior to the pistons
reaching top dead center on the compression
stroke. The fuel ignites during compression.
The pilot fuel needed to ignite the gas
is extremely small when compared to the
amount of natural gas utilized to generate the
electricity. Full-load dual-fuel pilot fuel consumption
is approximately three gallons per
hour per unit compared to full-load operation
diesel fuel consumption of approximately
850 gallons per hour per online unit.
Even though each engine is capable of
operating on liquid fuel only, the HBGS air
permit only allows 1,000 hours of diesel operation
on a rolling annual basis. For examwww.powermag.com
ple,
10 engines operating at the same time at
any load in diesel mode can only operate for
100 hours. In addition, the facility is only allowed
to operate an engine in diesel mode for
certain conditions listed in the permit, such
as during gas curtailments, testing, and routine
maintenance tasks that cause common
gas supply components to be out of service.
The engine control system allows a
seamless transfer to full-diesel operation,
if the control system detects combustion
anomalies or if gas flow is suddenly interrupted
to the engines. Because of the limited
amount of diesel-mode operation this article
will focus on issues resulting from dual-fuel
operation only.
POWER | July 2017
http://www.powermag.com
POWER July 2017

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