On many combined cycle projects, the major decisions about boiler chemistry are left until after the plant has been designed, equipment is procured, and construction is well underway. However, the best time to make these chemistry decisions is in the design phase of the project. That enables the engineering, procurement, and construction (EPC) contractor to design the plant that best fits the selected chemistry program (Figure 1).

1. Water treatment decisions. The EPC contractors should design the plant that best fits the users’ selected chemistry program. Courtesy: Colleen Scholl, HDR Inc.

Phosphate Versus Oxidizing, All-Volatile Treatment

For example, consider the selection of a phosphate program versus an oxidizing, all-volatile treatment (AVT-O) program. Of these two, the phosphate program requires more-responsive instrumentation and controls, because of the potential problems of phosphate carryover and hideout. If the EPC contractor has a priori knowledge that phosphates will be used, its engineers can specify highly responsive pH and phosphate instruments, and can ensure those instrument signals are transmitted to automated chemical-injection pumps that feed into multiple injection points (Figure 2).…

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