How to Dispose of NCG and TRS, 1998 Engineering Conference Proceedings

Jorgen G. Hedenhag, AirPol Inc.

Dan Banks, Banks Engineering, Inc.

Public concern, environmental legislation and regulations have forced the U.S. pulp mills to continuously reduce the emissions of particulates and acid gases to the atmosphere. At Kraft mills specific compounds have received attention lately. They are Non-Condensible Gases (NCG) and Total Reduced Sulfur (TRS). The first attempts at disposing of these gases were to incinerate them in the lime kim or in the power boiler. There are several disadvantages to this approach, such as long transportation distance from source to disposal point, and possible detrimental effects on the combustion source and the pulping process. Scrubbing of these gases also has its problems.

The incineration process converts the TRS compounds in the NCG to sulfur dioxide (SO subscript 2) and a small amount of sulfur trioxide (SO subscript 3). In those cases where the amount of SO subscript 2 generated exceeds the total allowable amount for the mill, an SO subscript 2 scrubber is required. This scrubber will have to be sized for the total flue gas volume from the combustion device. The gas volume from a dedicated incinerator is several orders of magnitude smaller than that from a lime kiln or a boiler, and will thus require a smaller scrubber.

The dedicated NCG incineration system offers operating personnel a way to isolate by-product disposal from the primary functions of the mill. The unsteady nature of NCG streams may cause problems when the lime kiln or the power boiler are the primary disposal devices. But does a dedicated incinerator mean smooth sailing ? According to reports from the field, problems still exist, This paper includes a brief overview of the different options, followed by a sampling of field problems and solutions from various installations.