Environmentally safe pumping of liquid tar and pitch
Tar and pitch are environmentally hazardous products, emitting cancerous vapours to the surroundings. Pumping these liquids thus require a seal-free pump. Both liquids have to be pumped at increased temperatures and they contain abrasive coke. Therefore they have to be heated and bearings must be wear resistant.
Tar is often transported by ships. The pumps on-board bring the tar to a storage tank from which it is pumped to a distillation tower where it is fragmented. During this process about half the tar ends up as pitch.
Pitch is among others used to produce electrodes for the aluminium industry. Normally the pitch is circulated in a ring-main by means of a 6-in pump. From the ring main a 2–3-in pump doses the pitch through a mass-flow meter to the mixers. The dosing pumps are frequency controlled.
This system looks simple but there are lots of details that have to be correct to avoid damaging the pumps. Koppers Denmark AS are specialists in constructing pitch systems including Rotan magnetically driven pumps with bearings in solid tungsten carbide, and they market these applications in Europe, South Africa and the Middle East.
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DESMI A/S is based in Nørresundby, Denmark. www.desmi.com
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