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GCI TECH NOTES©


Volume 11, Number 3           A Gossman Consulting, Inc. Publication       March 2006


This is part of a series of GCI Tech Notes focusing on the early development of the hazardous waste fuels programs during the early 1980s.  I was hired as the facility manager for the first commercial hazardous waste operation at a cement plant in early 1980.  Many of the developments in storage, processing, testing and use of hazardous waste fuels were the result of work done at a handful of plants in the early and mid 80’s.  Look for issues to include topics on storage, lab testing methods, processing and the impact of HWF on cement product quality and production.

Tank Farm Design and Operation – The Early Years

by
David Gossman, Gossman Consulting, Inc.

The first permanent, professionally designed tank farm for storage and feeding of hazardous waste fuel at a cement plant was built in 1980 at the General Portland Cement plant in Paulding, Ohio.  Because General Portland was a company with headquarters in Dallas, Texas with connections to the oil industry it was natural for the company to use an engineering firm with oil industry experience to design the system.  While the operation set a new standard for the time it was not without difficulties and a significant learning curve.

The original tank farm had four 25,000 gallon tanks with 7hp side-mounted agitators.  The concrete secondary containment system did not have anything more than a stone floor and included an oil/water separator on the drainage system.  Tanks were set on ring foundations rather than solid slabs. Differential pressure level indicators and alarms were part of the original design as were impeller-style flow meters.  Obviously, changes were made – some very quickly.  The flow meter shut down and stopped the flow with the first truck we tried to offload.

Another interesting early feature was that all trucks were offloaded with truck-mounted pumps; usually PTO driven Roper pumps, although some were hydraulically driven Blackmere pumps.  Either way, the hoses that connected the truck to the facility operated under pressure, not suction, as is currently the case, and they required draining at the end of each truck unloading.  Most trucks actually provided their own hoses as well.  The facility used a sealed concrete sump to drain hoses and hose ruptures were known to occur.   All material was filtered through a large basket filter. The filter was two feet across and an early improvement that I installed was a winch and pulley system to lift the lid off the filter.  When I first started off-loading trucks in Paulding, the plate steel lid was heavy enough that I could barely get it off and on the filter by myself.  Similarly, the filter was also large and cumbersome so the winched pulley system was a big improvement.  On at lease one occasion the filter was over-pressurized and sprayed waste fuel.

From the beginning centrifugal pumps were used to pump fuel from the tanks to the kiln through a loop.  Because of the size of the pumps and recirculation loop the early fuel spec for viscosity was about 32cp max, much lower than today’s typical max of 100-300cp.  Maintenance of the pumps was an early headache.  The fact is that an extra large pump operating at a low speed is the way to minimize wear and tear with the abrasive materials that have always been found in hazardous waste fuel.  That was a lesson learned early in the process.

Early facilities at cement plants did not have grinders – if the material would not pass through a filter it was considered out of spec.  Eventually market and regulatory pressures required that systems have the ability to grind solids instead of filter them.  Early systems included Greerco grinder-pumps and Muffin Monsters.  One of the early systems I designed for the Clarksville plant included a motorized Sarco strainer that sent only that portion of the stream that did not pass the filter to the particle sizing system.  Today’s systems that require all the fuel flow to go through the grinders continue to create maintenance headaches.

A problem that has occurred over the years a number of times is plugged pipelines.  This can happen for a number of reasons including:
·    Polymerization or thickening of material upon cooling
·    Laminar flow in pipes that allows solids to settle out
·    Reaction of materials resulting in solidification or polymerization

It is important to realize that the viscosity of hazardous waste fuel is non-Newtonian in nature. That means that the viscosity changes depending on the sheer rate.  Usually, but not always, the viscosity of HWF is higher at low sheer rates.  That is part of the reason it is sometimes hard to get HWF to flow using just a gravity feed and the reason it is so easy to cavitate a pump while starting up a HWF system.  Systems and procedures for removing air from lines are important to safe operation and the minimization of associated damage to pumps.

Another early feature of the first HWF tank farm in Paulding was the use of activated carbon to control vapor emissions.  The design firm, familiar with controls for oil storage, was not aware of the incompatibility of activated carbon and ketones such as acetone and MEK.  This was another system that required early intervention to avoid an accident and fire.  I am aware of at least one HWF facility that had a fire in their carbon canisters because they were unaware of this potential.  I continue to advocate the use of conservation vents and vapor balance systems for primary control of fugitive emissions from HWF tank farms.  If additional levels of control are required the use of refrigerated condensers or pressure tanks may be warranted.  Another early practice that should be avoided is the use of air to transfer fuel or flush lines.  Bubbling air into a tank of HWF can create a highly explosive atmosphere in the head space of the tank and the bubbles moving up through the liquid can build up a static charge creating the spark that sets off the tank.  Line flushing should be done with nitrogen.  Many facilities now have liquid nitrogen tanks on site and use that nitrogen for flushing lines.

Please contact David Gossman at 847-683-4188 or by e-mail at dgossman@gcisolutions.com for additional information – or if you have memories to share.