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PUMPING COAL TAR:  SELECTING THE RIGHT PUMP(S) AND MATERIAL

Joseph E. Higgins, P.E., L.S.P., Innovative Engineering Solutions, Inc., Boris Dynkin, P.E., Innovative Engineering Solutions, Inc.,
Michael Lotti, P.G., L.S.P., National Grid

Recovery of coal tar at former manufactured gas plant (MGP) sites has been problematic due to varying viscosities of the coal tar and incompatibilities of pump and piping materials with the coal tar. Removal of recoverable coal tar is frequently the primary driver for remedial response actions at former MGP sites. However, coal tar recovery is frequently easily dismissed as not possible for various reasons including pumping difficulties, material incompatibility and recovery inefficiencies due to generation of large volumes of coal tar and water emulsions, resulting in high disposal costs.

High shear pumps may emulsify the coal tar and water, rendering above ground separation of the extracted fluids problematic which may result in increased disposal costs. Suction pumps are capable of recovering coal tars with higher viscosities, but may not achieve adequate recovery rates and are limited by suction lift. Pneumatic pumps are capable of recovering coal tars with varying viscosities at acceptable rates, but may also result in emulsions if the tar is aerated. Since coal tar and creosotes are highly corrosive, compatibility with various components in the different commercially available pumps may also result in frequent maintenance and high replacement costs. Further adding to these inherent difficulties is that coal tar properties and recoverability are different at each MGP site. During system design, it is advisable to build in flexibility with the system to allow for extended testing, evaluation and use of various pump types to allow for the most efficient and effective recovery of coal tar at various stages of the project.

As part of a field project for the recovery of coal tar at a former MGP site (which contained more than 100,000 gallons of coal tar present as a separate phase), we conducted an evaluation of various types of pumps including peristaltic pumps, float-controlled pneumatic pumps, pulsed pneumatic pumps, and submersible pumps to determine which pump was best suited for coal tar recovery. Initially, peristaltic pumps were found to be capable of recovering coal tar of varying viscosities; however, the coal tar recovery rate was fairly low. We ultimately selected pneumatic pumps and have recovered more than 35,000 gallons of coal tar in 18 months, and have reduced the thickness of coal tar more than 7 feet to less than 1 foot. During this period, we also encountered compatibility issues of the coal tar with various system components, and have replaced various critical system components with stainless steel.

One of our main conclusions has been that pumps with the least moveable parts are optimal for tar recovery. We have essentially redesigned and built our own pulse-controlled pneumatically operated pump to achieve continuous trouble free coal tar recovery. The paper will discuss the various available options for coal tar recovery and the necessary modifications to achieve success.

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