Grinder manufacturers adapt for a new environment.
by Kevin Bates
November 28, 2017

Oil and gas drilling and processing operations are arguably one of the harshest industrial environments into which any equipment can be deployed. These can be high risk and high reward operations with success and profitability closely linked to maximizing equipment uptime to maintain a consistent throughput of production. This performance is imperative within the oil and gas industry, which relies heavily on the movement of fluids in closed systems and can be slowed or brought to a standstill due to a clogged pump or valve.

Crude oil refineries and drilling sites are especially at risk because of the high solids content of slurries moving through these operations, particularly relating to storage tank bottom cleaning at refineries and the reclamation of drilling fluids at the drill sites. Pumps, centrifuges and liquid-solid separators, critical to keeping production moving in these operations, are subjected to extremely demanding industrial conditions under a constant onslaught of hydrocarbons like paraffins and asphaltenes and inorganic solids like rock, sand, rust and heavy metal oxides. Consequently, this equipment experiences a high incidence of interruption and repair, impacting production throughout as well as operational costs.

drilling siteImage 1. Crude oil drilling sites are at risk due to high solids content of slurries. (Images courtesy of JWC Environmental)

Increasingly, drill sites and refineries are now relying on powerful in-line, two-shafted grinders to protect their pumping systems as well as costly downstream processing equipment. These grinders are powerful enough to grind down rocks, wood debris and paraffin sludge to ensure pumps do not clog and that liquid-solid separators and centrifuges receive properly-sized content for separation. This enables them to operate at optimum throughout without interruption.

Crude Oil Tank-Bottom Sludge Removal

One of the most challenging issues for refineries is the development of methods to minimize the cost of removing and disposing of crude oil sludge in storage tank bottoms. Crude oil sludge from storage tanks is a multiphase water/oil/solid composite, composed primarily of heavy hydrocarbon deposits, paraffins and asphaltenes and possessing a semisolid physical state. It is produced under normal storage conditions by the gradual sedimentation of heavy oil components, varying in consistency, density, thickness and composition across the whole tank bottom. Inorganic solids in the crude oil, such as clay, silica, calcite and corrosion-produced residues contribute to this process, bringing more hardness and higher density to the deposit. The accumulating sediment compacts, resulting in a thick layer of sludge, which is difficult to remove. The sludge can accumulate many feet in depth and up to 100,000 barrels in volume, which causes a gradual reduction in the tanks’ storage capacity, and uncertainty of available volume.

Refineries have inspection policies to verify the integrity of tank seals, flooring and roofs. To perform these periodic maintenance and inspection programs, the sludge must be removed. Tank cleaning, in the traditional sense, has involved opening or cutting a hole in the tank to remove the sludge, which is then openly transported to shaker screens, fed through a liquid/solids separator or centrifuge to reduce the volume of sludge waste, and subsequently transported to an off-site location.

crude oil sludgeImage 2. Crude oil sludge from storage tanks

This process, however, has come under scrutiny. Frequent throughput interruptions, in part caused by malfunctions with shaker screening systems, add time to an already lengthy method. Because it is a process open to the environment, sludge spills do occur, and volatile hydrocarbons are able to evaporate. This raises issues with plant emissions, which in some states has caused the process to be restricted.

In response to these concerns, the petroleum industry has developed better, safer, faster and less expensive methods for tank cleaning, allowing tank bottom hydrocarbons to be recovered and recycled back into the refining process. These systems are overwhelmingly closed-loop processes where, once removed, the hydrocarbons are recovered via enclosed external systems, such as centrifuges and liquid-solid separators.

Many of these closed-loop systems are designed to improve throughput efficiency by reducing the size of solids in the slurry-sludge solution to protect downstream pumps, valves, centrifuges and liquid/solids separators.

“In a closed-loop system for cleaning crude oil tanks, everything in that tank exits through a pump, before going to a centrifuge or liquid/solids separator, and then gets pumped back again into the tank under high pressure,” said Charlie Gioielli, industrial markets manager with Hahn Equipment in Houston.

“Crude oil sludge is hard, it crumbles, it settles fast, and it is abrasive. The pumps are producing in the vicinity of 1,500 pounds per square inch (psi), a lot of pressure that is being pushed through a relatively small passageway. Anything of size that gets in that passageway can block it and cause the pump to fail. That stops the throughput dead, right there, until it gets declogged, or if necessary, the pump repaired or replaced.”

“The solution to prevent the pump from clogging is to install an in-line grinder before the pump. We recommend dual-shafted, slow-speed, high-torque grinders that can handle up to 6,860 gallons per minute (gpm) and easily shred the toughest hydrocarbons, rust, rocks and whatever debris might come through from the tank.”