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Gas Works!

The latest developments in gas delivery technologies now offer far greater choice in the way that laboratories satisfy their gas requirements. Just a few years ago gas delivery methods were largely constrained by the volume of gas that the laboratory required but now it is possible for compact, on-site generators to supply almost all laboratory requirements - small or large volumes, continuous or periodic flows.

Laboratories with a large demand for gas may have their gas delivered in liquid form, from a manifold of gas cylinders, or even via a gas pipeline from an on-site production plant, usually set up by a gas supply company. For the low volume user, the most common method of delivery is bottled gas - gas delivered in high-pressure steel cylinders with a volume of around 50 Litres. These are normally filled to 200 Bar, which equates to about 10,000 Litres of gas.

While cylinders are the most widely used method of gas delivery, they have a number of disadvantages. Every cylinder, even though it is checked by the supplier, has the potential to cause serious injury - either through misuse or ignorance of the dangers involved in working with high-pressure gases. Even the simple task of moving bottles can pose a risk - they weigh in the region of 75Kg and should never be moved by a single person. Delivery of gas in cylinders is also expensive as it includes a charge for the gas, a charge for the rental of the cylinder, a delivery charge and a fixed charge depending on the supplier to cover administration costs. But the major problem with cylinders is that they run out - any system that requires a continuous supply of gas needs a switch over system between at least two bottles and a carefully controlled management system. Users also need a reliable supplier that will deliver when the gas is needed.

On-site gas generators are a welcome alternative - the user has complete control over the gas supply - once installed, the gas is always available in the laboratory where it is needed. On-site generators also have the advantage that they free the lab of bulky cylinders and avoid the hazards and time involved in moving cylinders into and out of the building.

There are many types of gas generator system and care must be taken to make sure that the choice of generation system is suitable for the laboratory's requirements. GRI Contract Services, through their agreement with Products of Technology Ltd, a Scottish firm specialising in gas generation systems, can advise on the types of generation system available and the best options for each installation. The gases that can now be produced on-site include; nitrogen, oxygen, hydrogen, hydrocarbon free "zero air", dry air and mixtures.

There are also generators suitable for specific applications. The NG-LCMS system, for example, is a nitrogen generator especially designed for liquid chromatography mass spectrometry. This new "intelligent" nitrogen generating system produces nitrogen with a purity of 99.95% on demand and shuts down when not in use. Compact in design, the generator easily fits beneath a standard laboratory bench.

For a guaranteed continuous supply, the GA range of nitrogen generators are useful for a range of applications across the pharmaceutical, electronics, food processing, optical, printing, automotive and medical/life sciences. There is no chance that the gas will run out, making them ideal for critical processes. There are twelve different machines in this series with flows up to 120m3/hr and pressure and purity suited to individual users' requirements.

Other gas generating systems in the GRI portfolio include; the Chrysalis™ hydrogen generating system and the Zero Air purifier. The Chrysalis system produces delivery pressures of up to 200 psig (1380kPa) making it suitable for both "fast" and standard GCs. Zero Air is a new air purifier, which reduces hydrocarbon levels to less that 0.01ppm. In applications such as GC with flame ionisation detection (FID), Zero Air provides a lower and more stable baseline and higher signal to noise ratios for greater sensitivity and improved analytical performance.

The most important consideration when choosing a generator is to correctly specify its size - although many systems are modular allowing the user to add extra capacity when needed. The application requirements also have to be taken into account. The main difference between using cylinders or liquid gas supplies and an on-site generator is that the flow from a generator is fixed whereas the flow from a cylinder or liquid supply can be varied. Flow restrictions can easily be overcome in a gas generating system, however, by making sure that the gas generating system is the right size and by adding a buffer tank.

There are three main points to be considered when selecting a gas generation system:

• The maximum and minimum pressure, flow and purity requirements of the equipment that the gas will supply.
  
  
• If the application is already being supplied by a traditional method - what is the pattern of use of the existing gas supply? This may vary from the actual application's requirements highlighting operator induced differences in gas usage or even revealing that there is a leak in the present system
  
  
• How will gas consumption change in the next few years. Are there any plans for expansion requiring greater capacity in the future?

The size and cost of a generator can be kept to a minimum by careful consideration of the application's needs. If the equipment does not require a constant flow then a generator producing the average flow rather than the peak flow can be sized along with an appropriate buffer tank. Purity is also and important factor, the size and cost of a nitrogen generator, for example, can be cut by approximately 25% by reducing the purity from 99.9% to 99%. This reduction allows the same flow to be handled by a smaller and cheaper generator.

Whatever a laboratory's gas needs, on-site gas generators are an important option. Able to save space, time and money they also offer peace of mind with no dependence on outside sources for critical gas supplies. GRI also offers a rental or leasing schemes for maximum flexibility.

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