Mission: Lower Emissions

At PSNH, we're on a mission to lower emissions, spending well over $100-million in the last 13 years on power plant technologies that have had a dramatic effect on reducing pollutants such as sulfur dioxide and oxides of nitrogen.

PSNH also makes great effort to calibrate and monitor emissions from its power plants. Probes and measuring systems in each power plant accurately measure emissions every few seconds and, in many cases, alter the operation of the plant to ensure the lowest levels of emissions possible.

In signing The New Hampshire Clean Power Act, PSNH reached a first-in-the-nation agreement with the state and a diverse group of key environmental organizations that sets specific reduction targets for several pollutants. Following are key pollutants, how they effect the environment as well as the various measures and technologies that PSNH is using to help reduce them:

• Fly Ash
• Oxides of Nitrogen
• Sulfur Dioxide
• Carbon Dioxide
• Mercury

Fly Ash

A large component of smoke is minute particles of ash. As such, it's makes up the majority of the stuff you see coming out of the chimney for your fireplace. It used to be a visible component of the smoke coming out PSNH power plants. But beginning in 1989, PSNH began putting devices called electrostatic precipitators (ESPs) on its smoke stacks.

Electrostatic precipitators are huge devices mounted in the power plant's exhaust. Plates inside the ESPs are charged negatively and the fly ash is charged positively which attracts the ash to the plates. Periodically the fly ash is dropped into a hopper and the fly ash is trucked to cement plants where it is used as part of the manufacture of Portland cement.

Though the typical cost of an ESP is more than $XX million, they work well: Today, the visible smoke coming from PSNH stacks is, in reality, almost entirely steam.

Oxides of Nitrogen

A byproduct of high-temperature combustion, oxides of nitrogen contribute to greenhouse gases, acid rain and changes to the ozone layer. Since 1995 PSNH has reduced oxides of nitrogen using several methods, including the installation of low NOx burners, as well as Selective catalyst reduction (SCR) and selective non-catalyst reduction (SNCR), both of which employ ammonia injected into the power plant's exhaust to convert nitrogen oxide into harmless nitrogen and water vapor.

Sulfur Dioxide

Sulfur dioxide contributes to acid rain and is a byproduct of burning coal. In the early 1990's PSNH lowered sulfur dioxide emissions by 40% simply by switching to low sulfur coal. Sulfur dioxide emissions are lowered even further when PSNH burns oil and natural gas to create power. And the landmark agreement PSNH signed with New Hampshire this year will lower the output of sulfur dioxide even further.

Carbon Dioxide

A product of any combustion process, carbon dioxide is created by automobiles, trucks, home heating units and by fossil fueled power plants. At this point there is no known way of reducing carbon dioxide emission except by reducing combustion and therefore the corresponding amount of electricity.

Mercury

While it is known that small amounts of mercury is present in coal, what is not known is how much of the mercury is entering the air from the stack and how much is deposited in the fly ash that is trucked away. Currently, the Environmental Protection Agency is determining a standardized method for measuring mercury output and will issue regulations governing mercury reduction if required.