Going with the flow

Step-changes in process technology As well as the regular development of relatively minor improvements are enabling operators to continue to meet changing regulatory requirements and to run their plants more efficiently.

Many process operators, especially those in the offshore oil and gas industries, are investing in flange guards and safety shields, to help compliance with the latest regulations, such as ATEX137 and DSEAR.

Safety shields wrap around flanged joints or couplings in pipelines, and completely prevent lateral spray-out: they were originally developed for use on fuel pipelines in marine applications, such as ships’ engine rooms, where any leak could potentially spray onto a hot surface and cause a fire.

More recently the shields have been adopted by chemical plants to improve personnel safety, preventing any spray of corrosive or dangerous chemicals from any gasketed joint.

For pipework containing acids or alkalis, Allison Engineering introduced the Spra-Gard shield, fitted with an indicator patch: should any acid or alkali leak out from the joint, the indicator colour change provides an immediate visual warning signal.

Allison Engineering stresses that the shield is designed to prevent the spray-out, but is not designed to contain the leak, it is just controlled. So the leak must still be visible, so that it can be discovered and eliminated. Special shields have been developed with collection pots or drains, with a built-in leak alarm. Other special designs include units to cover valve bonnets.

Intertek-Epsilon, an accredited DSEAR and ATEX implementation company, has frequently used or recommended Allison spray shields, wherever there have been potential flammable mist spray issues. Their use, it said, enables a reduction in the size of the hazardous area classified zones.

Any company using or storing hazardous liquids in large quantities is facing increasingly tough regulations to screen or otherwise prevent spray-outs from pressurised pipelines, notes Intertek-Epsilon. There is, it added, growing pressure from insurance companies for their installation, particularly on sites where an incident has occurred.

Control of spray coating volumes applied on a variable speed production line or the control of the coating thickness has always proved difficult. Adjustment of line pressure is one option, but this, typically, affects droplet size and spray pattern, as well as delivered volume, and any variation from the standard set-up conditions usually results in unsatisfactory spray conditions. The PWM system also solves the problem of control of very low spray volumes, since at low duty cycles the delivered volume can be as low as only 5% of the normal nozzle delivery. This equipment is now being applied in food industry applications, adjusting flavourings for potato crisps, oil sprays on chickens prior to cooking as well as chocolate spray deposits on items such as cakes and nuts.

Spray nozzles are more frequently met in process applications where a spray ball is used in tank-cleaning operations. The static spray ball has been in use for around 100 years, but for efficient cleaning requires large volumes of water, high chemical concentrations and extended running times.

A more modern option is the rotary jet head (RJH) design from Alfa Laval. Using relatively low pressures, the cleaning fluid itself is used to drive a turbine that rotates the cleaning nozzles around both vertical and horizontal axes. Cleaning time is reduced to minutes rather than hours, and the RJH is a standard installation on beer, wine and food production plants.

Trials at dairy and food processing plants have shown how the RJH can replace a standard spray ball and reduce the cleaning times and rinse cycles required.

In a raw milk silo, a single Alfa Laval Toftejorg SaniMega RJH machine achieved sufficient savings on cleaning chemicals to pay back the cost of the installation in six months, in addition to reducing cleaning cycle time by 30% and water usage by 40%. In a food processing plant, the time savings resulting from replacement of the spray ball allowed a production increase equivalent to running a further 770 batches of soup in a year.

Accurate control of fluid delivery for a batch quantity or controlled dosing of process additions can be achieved by standard control inputs to pumping systems. One technique is to use a speed control on a peristaltic pump as this offers high levels of flow repeatability and also eliminates the need for any seals, valves or metering systems. And it can be used across a range of industries.

In the cement industry, grinding aids such as glycol, amines and acetic acid help the cement particles to flow efficiently. A US-based cement manufacturer has used a Larox Flowsys LPP-D15 pump controlled by a variable frequency drive system to accurately dose polyglycol into the final cement grinding stages, which has reduced the energy needed and increases throughput.

Shinetsu, a major silicon wafer producer located in Livingston, Scotland, had experienced reliability problems in pumping the silicon waste from the cutting of the wafers. In particular, the heavy and extremely abrasive silicon waste was causing severe problems in all pump types used to remove it after the production process.

To resolve the problem, the company selected a peristaltic hose pump from Verder, which can handle extremely abrasive products. In trials, the pump managed to perform for eight weeks without failure, with the process of changing the hose established at six-week intervals. This arrangement, said Verder, ensured that the peristaltic pump never failed in service and wafer production continued uninterrupted.

Back in the energy sector, a world first was achieved on the parallel Qatargas 3 and 4 projects: the well-head platforms that will deliver the gas to the liquefaction plant are constructed using hundreds of Techlok Clamp connectors from Vector International.

Many of the connectors needed the corrosion-proof protection provided by the specially formulated Alloy 625, which is applied by weld overlay cladding. The 12- and 26-inch connectors for these LNG projects were supplied to standard designs, but the Qatargas 3 and 4 projects also called for some 42-inch connectors: such large connectors had never been built before. Cladding this size of connector was undertaken as usual by Arc Energy Resources, and because of the large size, the units were stress relieved: AER has calibrated heat treatment furnaces suitable even for this size of component.

Even higher pressure retention is needed on the chemical injection skids used on oil platforms, such as the Chevron Tahiti field in the Gulf of Mexico. For this application, the skid, built by Test Automation and Controls, designed to operate at 15,000psi, is believed to be the largest ever such skid produced. Parker Instrumentation halved the space and weight budgets for a double block and bleed valve function, by providing an uprated version of its standard 10,000psi manifold, fitted with the Parker MPI compression tube fittings. Eliminating the normal arrangement using separate valves and anti-vibration glands greatly reduced the number of joints and potential leak paths.

Kevin Burke of Parker said: “The size and weight reductions contributed by this manifold have helped to reduce the topside equipment budget. The manifold also helps to eliminate threaded connections, a common source of reliability problems.”