STEAMED up

Over the past 15 years, trace heating technology has advanced to the point where modern systems are more convenient and cost effective than ever before. Steam tracing systems installed more than 20 years ago may still be effective, but they are seldom as economical as new steam systems, which offer efficient, reliable, low maintenance operation, or as aesthetically pleasing as modern electric systems.

At Spirax Sarco, we believe the most cost effective solution is to upgrade the existing steam system to achieve optimum performance - at lower installation and operating costs than a new electric system.

Steam tracing continues to dominate new projects, particularly within the oil and chemical sectors, although electric systems are more suited to low temperature applications, for example for heat sensitive products, such as caustics, and for short runs (2-3m) of pipe.

Several advances have swept away many of steam's former disadvantages:

* The deployment of prefabricated - rather than custom built - compact forged steel manifolds makes installation both easier and cheaper.

* Quick fit steam traps enable easy maintenance. The universal connector type trap is simple to remove and integral piston valves in the connector cut the number of pipeline components.

* A common misconception is that only the most basic on-off control is possible for steam tracing, but self acting temperature controls provide accurate modulation of the steam supply.

* Electronic systems can automatically monitor all steam traps on a given site. The plant operator can be alerted when the tracer line requires attention.

* Heat conductive cement, employed as a fillet between the tracing line and the product pipe, increases the heat transfer rate, allowing the installation of smaller and fewer tracing lines.

HEATING BILLS

Where steam is already used on site, upgrading such a tracing system will almost certainly have a lower cost than installing an equivalent electric system. Steam and condensate return lines will already be in place and can be used for the new tracing system, keeping down the cost of installation.

As the energy cost of both steam and electric systems rapidly dwarfs the original capital cost, this must be a prime consideration. Steam is often generated on site for process applications, leaving low pressure steam, which is often regarded as free energy, available for tracing. However, a more meaningful comparison is made by calculating the costs of a gigajoule of energy for both media.

The table (below) illustrates the difference in energy costs for these media. The energy costs have been calculated using data from the DTI's Energy Trends bulletin. Based on a typical steam system, assuming that boiler feed water is at 80iC, boiler efficiency is 80 per cent and steam pressure is 7barg. One gigajoule of electrical energy costs up to 5.5 times the steam equivalent.

High temperature tracing will almost always be best met with steam tracing. Above 160iC the capital cost of electric tracing becomes significantly greater and the energy costs are also high. Apart from costs, there are a number of other factors to consider.

Steam systems offer great flexibility and could trace a completely different product should it be introduced on the line at a later date. Electric systems tend to be installed to match the particular heat requirement, which may not suit the needs of a different product. Steam cleaning of pipelines to prepare them for different products can easily damage the electric tapes.

If the tracing system is exposed and prone to damage, steam should be considered because it is more robust than electric tracing tapes. Moreover, as a system's insulation deteriorates, its efficiency is reduced and the heating demand rises. Electric tracing will be unable to meet this higher demand. Steam tracing, with its temperature directly related to its pressure, compensates easily.

Installers may effect significant cost savings by upgrading an old steam tracing system to modern standards - often at very little capital cost. The longevity of steam tracing systems in particular opens up the possibility of investment with short payback times.

{{The main upgrades include:

* Automatic temperature controls;* Universal connector steam traps;* Automatic steam trap monitoring;* Easy maintenance manifolds;* Improving insulation efficiency.}}

PREFABRICATED MANIFOLDS

An example of the cost savings that can be achieved with our compact prefabricated manifolds is an installation of £5000 worth of equipment at International Speciality Chemicals' (ISC) site at Hythe, Southampton.

ISC manufactures chemicals used in products ranging from contact lenses to adhesives. The manifolds, fitted with thermodynamic steam traps, have been installed throughout the steam distribution system on site. The system's main drainage points feed into the manifolds, providing compact condensate returns.

The forged carbon steel manifolds offer fast in-line maintenance. With the original manifold maintenance involved cutting out traps and valves and welding in replacements. Simplifying the procedure is critical for ISC with its estimated 850 traps on site.

`Changing traps is now hassle-free,' says Sean Leach, ISC's works engineer. `Previously, we had to move pipework to remove a trap. Now it's a quick job to close an isolation valve and disconnect the trap for maintenance.'

Each manifold port incorporates an integral piston type valve for reliable isolation. The valve's large sealing area does not come into contact with the media, and so cuts the susceptibility to dirt or erosion. Internals can also be replaced quickly, normally in under 5min.

Spirax Sarco's steam trap monitoring system, the Spiratec R16C, is a key element ensuring the safety and reliability of a low density polyethylene plant at Carrington, Manchester.

The plant's operator, Montell Polyolefins, a merger of the world-wide polyolefin interests of Shell and Montedison, needs to monitor remotely a critical part of the steam trace heating system, which maintains temperature of pipework that contains polymer.

`The pipework is located in the reactor cell, which is not accessible during normal operation,' explains Malcolm Twite, Montell's senior mechanical engineer. `We need to verify that up to 45 steam traps are operating correctly and not failing in the closed position.'

If a trap fails while closed, condensate backs up, causing the pipeline to cool and the polymer to solidify. This could interrupt the production process and result in costly downtime.

`Spirax Sarco was able to offer its Spiratec R16C system. This was accepted and the equipment delivered within four weeks of order placement. Trouble-free installation and commissioning took place within a further two weeks and the system continues to operate successfully, so playing its part in ensuring the plant's safe operation.'

A single Spiratec R16C monitor can continuously check up to 16 steam traps of any make or design, immediately alerting the type and locations of failure and which trap is affected.h

Roger Ferryman is oil & petrochemicals manager at Spirax Sarco, Charlton Kings, Glos.

{{Comparative energy costs

Tracing Cost of Cost/GJ mediummedium fuel tracing medium

Electricity 3.1p/kWh £8.64Steam from heavy oil £72.80/t £2.14Steam from natural gas 0.5p/kWh £1.74Steam from coal £1.21/GJ £1.51Pass out steam Free Free

Source: DTI; costs do not include installation}}

`Cleaner' electric tape trumps steam

Electrical heating system supplier Heat Trace, of Stockport, has installed an electric heat tracing system on a long jetty oil pipeline for Tianjin Voray, in Tianjin, China writes Matthew Peach.

The £120 000 project involves 14km of the company's Longline flat foil heating tape and control and monitoring equipment for heat raising and temperature maintenance in the 300mm diameter pipeline. Heat Trace claims that Longline was chosen in preference to a steam system because of its cleanliness and its ability to operate from one power supply point.

The control panel at Tianjin Voray features the Powermatch self-regulating controller, Watchdog circuit health monitor, and Centurion proportional electronic controller. The heating cable can raise the pipeline temperature to 230iC, and implementation of Heat Trace's Powermatch control system maintains the temperature to within *1iC.

Often, the most important consideration when heating long pipelines is the number and location of electrical supplies, which are normally available only at pipe ends. In this case, a 600V, three-phase supply was employed. The cost of providing intermediate supplies is prohibitive, so heating circuits must be designed for long route lengths, each of up to about 5km.

Long pipelines typically require hundreds of kilowatts to maintain pumpable temperatures. Power/Energy management minimises operating costs, maximum demand and eliminates expansion and contraction, which can result in failure of the thermal insulation or heater.

A single Longline HTS3F tracer, which has three conductors, is suitable for shorter circuits, up to, say, 1km. Multiple large single conductor Longline HTS1F tracers cater for longer circuits, up to 5km.

* Heat Trace has developed a new Trace heating Energy Management, Performance and Optimisation system - known as Tempo. Tempo is a computer assisted energy management and auditing system for heat tracing installations where optimum safety, energy efficiency, system integrity or system life may be desired.

The system comprises software designed to operate on Windows 95 or NT. The result is a `fast, powerful system that can stand alone or be integrated into an existing plant SCADA or DCS system,' claims Heat Trace.

Tempo receives signals from Heat Trace's electronic control equipment, with the data being converted into trend and performance reports and displayed graphically. It can also depict the data as an alarm and produce a forecast for recalibration of control equipment.h

Piping hot: Heat Trace installed an electrical system for Chinese oil company Tianjin Voray