NLB Corp.

The case for water jet tank cleaning

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Courtesy of NLB Corp.

To maintain a consistently high level of product quality, today's processing plants must ensure that their tanks and reactors are thoroughly cleaned on a regular basis. The direct expenses involved can be substantial, and adding indirect costs {e.g., downtime and compliance with safety and environmental regulations) puts extreme pressure on tight operations budgets.

To meet this challenge, more and more companies are cleaning their tanks with high-pressure water jetting. It removes hardened deposits thoroughly and economically (often saving thousands of dollars), and keeps operating personnel safely out of confined spaces.

The basic idea is to put a 3-D water jet head into the tank instead of a person. While the head rotates horizontally, its two high velocity water jet nozzles spin vertically, resulting in complete, 360 degree interior coverage. These nozzles are driven by the reaction energy of the high-pressure water (from 4,000 psi to 20,000 psi), which cuts through virtually any product build-up on the sides of the tank, and even in its crevices.

Hardened paint, resins, epoxies and chemicals, as well as rust and scale, are removed in minutes and rinsed away. When a tank is large — e.g., 20' or 30' high —the head is mounted on a telescoping lance.

Here are some of the benefits.!

Manual cleaning is slow and labor-intensive, and production cannot resume until the job is complete. In one documented project, water jets reduced downtime for cleaning a 3,000-gallon reactor from 14 hours to just 4 hours. The downtime hours shrink proportionately with tank size - a 20,000-gallon reactor that was normally out of commission for 72 hours came back online in just 8 hours when cleaned with water jets. And the reductions in labor vs. manual cleaning are even more significant, as seen in the accompanying table.

Protecting employees from risk is not only common sense, it makes good business sense. Preventing accidents can help control medical costs and reduce downtime. According to OSHA data cited in Modern Bulk Transporter in 2002, nearly half of tank cleaning accidents are caused by thermal burns or chemical contact. Other hazards associated with tank cleaning are poor air quality, extreme temperatures and noise, as well as everyday slips and falls. These risks are facing increasing scrutiny, resulting in new Permit-Required Confined Spaces (PRCS) standards and other OSHA regulations.

Compliance with all these regulations can be complex and time-consuming. Staying out of tanks altogether makes life easier for managers as well as operating personnel, and automated water jet cleaning makes this possible. Also, since water jetting uses absolutely no chemicals or caustics, no one needs to be exposed to potentially hazardous substances or fumes.

Environmental responsibility
Water jetting also extends these advantages to the workplace at large, and even the surrounding community. Since the power of water jetting comes from nothing but high-pressure water, nothing harmful is released into the atmosphere. This also simplifies disposal and reduces associated costs, both direct and indirect (e.g., compliance with fewer regulations, as noted above).

Because of the savings from reduced downtime and lower expenses for labor and disposal, water jetting's long-term costs are probably the lowest of any tank cleaning method. The initial investment for the 3-D head, lance and high-pressure pump unit can be substantial, but since NLB water jetting can save a plant hundreds of thousands of dollars a year, the payback period is short. Improved safety and product quality (thanks to the thorough cleaning) also can lead to significant long-term cost savings, although they can be harder to quantify.

3-D water jetting has consistently demonstrated its effectiveness in removing all sorts of resins and similar products, including ABS, PVC, PS, PU, BR, CR, PVAC, SAN, IR, NBR and SBR. One NLB customer who was accustomed to spending more than 100 hours to clear a 25' vessel of 7'-thick coke found that he could do it in just 20 hours with water jets. The process is used successfully in large tanks and reactors (e.g. 40,000-gallon) and in the smaller, reusable stainless steel totes often used for shipping chemicals. One chemical company doubled its cleaning output with an automated NLB system, from 55 totes/day to 110/day.

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