General

New heating system at North Omaha plant a step toward decarbonization

As OPPD continues taking steps toward decarbonization, a project is underway at OPPD’s North Omaha Station (NOS) to switch from coal to an electric heat source to warm the plant when units are not in service.

Crews are installing a new electrode auxiliary boiler to provide electric heat to the plant’s heating system. The new boiler also provides steam to start up units when they need to run. The steam boiler is also a crucial early step in OPPD’s decarbonization strategy.

The electrode boiler project started last year under Chris Scofield, the project manager and a design engineer at OPPD.

Auxiliary boiler a new heat source

For 70 years, NOS used steam from coal-fired boilers to heat the plant. That steam also started the natural gas peaking units in recent years.

However, to align with OPPD’s decarbonization goals and plans to phase out coal, NOS needs a new, non-fossil fuel heat source.

“We evaluated several different options,” said Scofield. “Ultimately, we determined that an electrode boiler was the way to go. The electrode boiler also supports our decarbonization plan, which is a plus.”

The auxiliary boiler is large – more than 27 feet tall. There isn’t much wiggle room at NOS, so making the boiler fit took time and effort.

“It has been tight, fitting the new boiler in,” said Scofield. “But the work has gone well.”

The boiler’s height required placing it in a maintenance work area below the turbine deck to maintain full function of the plant’s main turbine building crane, Scofield said.

OPPD’s maintenance department helped with the boiler installation. Contractors removed a 13-foot by 26-foot slab of concrete floor.

OPPD maintenance crews played critical roles in supporting the outside contractors as they installed the new system.

Conversion

NOS converted units 1, 2 and 3 to natural gas in 2016 and fitted units 4 and 5 with emissions-control measures to allow them to run on coal but with lower emissions.

OPPD will convert units 4 and 5, the two newest units at NOS, to run on natural gas, and the utility will retire the older three units.

Work is underway to install new supporting components at NOS, including more than 2,000 feet of piping, 3,400 feet of electric cable, and 12 pumps and motors to support the new system.

Steam produced by the boiler will interconnect with existing piping within NOS, producing steam for the existing heating system and for starting one of the gas-powered units.

Clean, demineralized water is used to produce the steam, similar to the way distilled water is used for the steam function of your clothes iron to keep mineral deposits from building up and causing damage.

Putting cool water into the boiler challenges boiler operation. In addition, cooler water can entrap gases that will degrade the boiler components. So a deaerator is used to heat the water with steam and remove dissolved gases before the water goes into the boiler.

“Unlike natural gas boiler designs, electrode boilers produce steam at a 99.9% efficiency at all loads, as a result there is minimal efficiency loss at lower loads,” Scofield said.

Timing

The final work on the new boiler will happen after OPPD retires units 1, 2 and 3 and converts units 4 and 5 to natural gas.

Once OPPD retires units 1, 2 and 3, it will replace the existing unit 2 transformer with another existing OPPD transformer, one that is compatible with the new boiler. Then the current unit 2 transformer will become a critical spare for other OPPD-owned generating units, “a win-win for OPPD,” Scofield said.

OPPD anticipates retiring units 1, 2 and 3 and switching units 4 and 5 to natural gas around 2026..

“We are planning on commissioning the auxiliary boiler shortly after the SPP approves the retirements of the oldest NOS units, currently planned for the end of 2025,” Scofield said. “Other projects are required to support the coal-to-gas conversion, but many of those cannot be installed until we stop coal operation.”