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PROJECT: Boiler Controls Upgrade Project

Three Erie City Boilers built in 1959 and each rated at 25,000 lbs/hr flow at 125 psig saturated steam were used to supply the steam energy requirements for a state prison on the west coast. A previous NOx burner and controls upgrade ending in 1998 was successful at meeting new lower stack emission requirements set by the local Air Pollution Control District. The 1998 controls upgrade installed the traditional mechanical jackshaft lever arm control system to position the fuel, air, and gas recirculation flow (GRF) damper. A number of safety, stack emissions, and operational problems arose out of the more traditional jackshaft design. This most recent boiler controls upgrade project corrected the previous deficiencies and provided added benefit.

Engineering provided a large range of services that included identification of the existing process & control deficiencies, establishing the design criteria (listed below), providing a control logic design that met the established design criteria, and overseeing startup and final commissioning.

The project criteria, successfully achieved, is stated below:

1. Safety Criterion:
Improve boiler safety by eliminating furnace over pressure transients.

2. Emissions Criterion:
Maintain stack emissions within current permit limitations under all operating conditions.

3. Efficiency Criterion:
Improve boiler and operating efficiency resulting in a net reduction of total fuel usage and steam plant electrical use.

4. Operating Criterion:
Extend boiler turndown to enable continuous firing at the lowest facility demand level.

To meet all four of the stated criteria, the next level of control sophistication was orchestrated in a design of the control logic philosophy, the controlled field devices, and the microprocessor multi-loop controllers. In summary, the design included upgrading the Plant Master control logic from pure pressure control to steam flow control, upgrading the boiler control system to a “fully metered” system, and increasing the usage of the multi-loop controllers including the addition of controlling boiler flue gas O2.

The final results exceeded expectations for all four project criteria. The most notable achievement being an estimated savings of approximately $140,000 per year in fuel and electricity due to a dramatic improvement in boiler process stability!