Aim for balance when designing wash racks

WHEN systems are fully balanced, a tank wash rack can operate at maximum efficiency and cost-effectiveness. It's easy to see the need for a balanced system, but getting there is the challenge.

Travis O'Banion, Trimac Transportation System, reviewed the various aspects of a balanced wash rack during the NTTC Tank Cleaning Council Seminar in Lake Buena Vista, Florida. Ideally, the process of achieving a balanced wash rack should start with the design of the facility and the initial training of the employees.

“We need the right equipment for the types of tank cleaning that will be done at the wash rack,” he said. “We need accurate data developed from impingement formulas and such when specifying pumps and spinners.

“In too many wash racks, pumps are being run on the left side of the pump curve. Pressure often gets more consideration than impingement during system design. Cleaners also need to be taught the meaning of pressure readings.”

He added that there is a tendency in the industry to try to make do with the least possible amount of equipment. “All too often, we don't use the extra pump or additional spinner that would do a more thorough job of cleaning or make the operation go faster,” he said.

Pipe diameter matters in the design of the wash rack, as do spinner type and size. Spinner tip size must be considered. Just as important is the spinner drop depth in the tank being cleaned. “If the spinner isn't at the correct depth, it will miss sections of the tank during cleaning,” O'Banion said.

Return pump capacity is critical. On the one hand, water can't be allowed to pool up in the tank because that will impede the cleaning process. On the other, it's important not to remove water too fast because that can lead to pump cavitation.

The products and equipment that will be cleaned are important considerations in the design of a balanced wash rack. Designers also should be aware of the types of cargoes that will be loaded after a tank is cleaned.

Other factors include anticipated tank cleaning volume, water quality, and wastewater treatment requirements. Air permit restrictions are of increasing concern in many parts of the United States. “You need to meet with state and federal environmental officials at the outset of planning for a new wash rack,” O'Banion says.

A wash rack must be operated and maintained properly to remain in balance. Thorough training and retraining are key to meeting these objectives.

Cleaning operators need to understand why, not just how, according to O'Banion. They need a clear understanding of company procedures and safety requirements. Technical factors, such as impingement formulas, should be covered during the training.

“We need to do a better job of teaching operators the importance of using the pressure gauges,” he said. “Pressure has a significant impact on the cleaning process, and we are just shooting from the hip when we don't use the gauges.

“We also need to teach operators that consistent flow rates (gallons per minute) affect impingement more than (pump) pressure. Operators need to know about proper cleaning chemical ratios and proper temperatures for various cleaning solutions.”

When considering wash rack maintenance, operators must be taught how to do a proper daily visual inspection and must understand filter cleaning and replacement procedures. They must know how to determine when spinners and tips need replacement.

Operators have easy access to vats to sample cleaning solutions. In addition, maintenance procedures for a balanced wash rack operation must include periodic calibration of cleaning systems.

Safety can't be ignored. Operators must understand how to avoid incidents and injuries, and they must be provided with appropriate personal protective equipment. Regular safety meetings are needed to maintain awareness. Wash rack systems must be designed and configured for safe operation.

Wash rack security is now of greater concern. Part of the design process for a new facility should include ways to limit access. Video surveillance may be needed in some locations.

Security procedures should include daily chemical and hazardous waste inventories. Yard checks of tank trailers should be conducted several times each day.

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