Southern African Natural Gas Advisory Service Service

An indicative summary of the natural gas network in Holland is likely to be as follows:

 transmission grid of between 200 - 1200 mm diameter pipelines with an approximate length of 4500 km's.

 regional network of between 50 - 400 mm diameter pipelines with a probable length of 7000 km's.

 9 compressor stations which raise the pressure of the natural gas to enable it to travel its long journey through the pipeline network system.

 80 metering and pressure regulating stations. These ensure gas fed from the high pressure transmission system into the regional grid at the correct        pressure.

 1100 gas transfer stations ensuring gas is at the right pressure for local gas distributors, large industrial customers and power stations.

 20 export stations on the country's borders: in the 1990's Holland was a major exporter of natural gas to Germany, France, Belgium, Italy and        Switzerland. A single export station typically handles 75 million cubic metres of gas throughput every 24 hours.

 LNG facility for natural gas storage and peak demand management

 telemetry, measuring and control technologies throughout the transmission network with a Control Centre to manage the system

 thousands of kilometers of local lower pressure pipe networks  bringing the gas to residential, commercial, agricultural and other users.

 underground gas distribution networks managed by local gas distributors who interface with medium and smaller gas consumers.

 metering in consumers premises and the provision of customer service by local gas distributors.

How is it stored and transported?

Natural gas storage

The ability to store natural gas adds another positive feature ensuring supply reliability. Traditionally, the transmission pipeline operators and local gas supply utilities provided storage services but today in many countries other players, such as gas producers, gas import operators and liquefied natural gas suppliers provide storage as well. In the U.S. and across Europe there are hundreds of underground natural gas storage facilities. This storage space can take several forms. The most common one is depleted underground reservoirs from which natural gas was extracted.

A good example is the Bain subterranean gas field underneath the Irish Sea that Centrica, a British Gas company, is considering in partnership with Gaz de France, to develop into a gas storage facility. Despite a possible cost of between GBP 300 to 350m this new storage field, if it is developed, will be only one fifth the size of the existing Rough subterranean storage facility which currently accounts for 70% of the UK's total natural gas storage capacity. As Britain becomes more reliant on imported gas and the supply flexibility from North Sea gas fields decline in coming years, such storage will ensure the country's future security of energy supply.

Other suitable facilities include aquifers which are large underground areas of water bearing porous rock; and, salt domed caverns. Salt dome natural gas storage is becoming widespread because gas can very quickly be injected or withdrawn to accommodate sudden fluctuations in demand.

In Holland they have constructed clusters of natural gas storage caverns at a depth of between 1000 and 1500 meters to meet gas demand at peak periods that provide a reserve of some 500 million cubic meters of gas (mcm).

Liquefied natural gas (LNG) is also increasingly used to provide storage to balance supply and demand. When natural gas is liquefied at very low temperatures and high pressure, 600 cubic meters of gaseous gas is reduced to 1 cubic meter in the liquid state. In Holland, as an example, they have built a storage facility for LNG 30 km's from Rotterdam. In the summer months natural gas is changed into a liquid state. When needed, this LNG stored in large heavily insulated tanks is turned back into gas and injected into the transmissions system.

Access to storage allows gas buyers in many countries to acquire low cost supplies on the spot market during off peak demand periods and to store the gas near its point of use for delivery during peak usage periods. Furthermore, the ability to store natural gas lessens the impact of production disruptions. As a powerful illustration of this, storage of gas and the hidden underground network of gas pipelines allowed the gas industry to maintain service to all markets without interruption despite the widespread damage inflicted by Hurricane Andrew in the USA on oil and gas facilities as it crossed the eastern Gulf of Mexico and coastal states in late August 1992.

The other major source of natural gas storage, are the vast natural gas transmission pipeline networks that now stretch across great swathes of the world. In the USA there are thousands of miles of interstate and intrastate pipelines with billions of cubic feet of daily natural gas capacity.  Similar pipeline networks exist for natural gas across North Africa, Western and Eastern Europe, various countries in the Far East, Australia and Russia.

In South Africa, PetroSA have gas storage facilities at their Mossgas gas to liquids (GTL) plant in Mossel Bay. Sasol also deploy their Mozambique pipeline as a massive gas storage system to manage the occasional plant shut downs.   

Transporting natural gas

With the greatly increased volumes of natural gas consumption in the world today, this would not have become possible without two major developments: one involving major infrastructure development; and, the other the industrial application of cryogenics (the science of low temperatures).

The infrastructure development has been the laying down of thousands of miles of natural gas transmission (and local distribution) pipelines, pressure stations and sophisticated monitoring and control systems.

Cryogenics on the other hand has enabled the large scale production and transportation of liquefied natural gas across oceans by sea.

Ship borne LNG has enabled huge quantities of natural gas to be commercially transported across oceans from the gas producing regions of the world to energy consumers elsewhere. As with the global trade in oil with bulk carriers travelling across our oceans, so today, a similar trade  exists with LNG. Specially designed and built liquid gas carrying ships are becoming ever larger and more common. LNG has become the preferred method for long distance, high volume transportation of natural gas whereas large diameter transmission pipelines are preferred for distances of up to 4000 km's over land and half that distance offshore.  

Where the distance between production fields and end users is greater than 2000 kilometers then LNG is often a viable alternative to laying a pipeline.

As well as LNG, natural gas is also transported (and stored) as compressed natural gas (CNG) which is transported at high pressure which is typically greater than 200 bars. Equipment for compressing and decompressing natural gas is less capital intensive for lower volume transportation needs than liquefaction and regasification plant required for LNG. With CNG, trucks and other carriers may transport natural gas directly to end-users or to pipeline distribution points.

The natural gas industry's proven ability to deliver natural gas produced from a vast resource base is a critical factor and technological success story.

Moving natural gas across continents from distant gas fields to a factory, power station or home nearby, is accomplished safely, quietly, invisibly and efficiently through thousands of miles of underground pipeline and local distribution systems.

In fact, compared with truck, train and electric transmission, natural gas transportation is the safest, most reliable delivery system of any form of energy.

Hurricanes, snow storms and excessively hot weather knock out above ground electricity supply networks, there have been two major international nuclear disasters in recent history impacting thousands of miles of the environment and all that lives in it, even renewable energy is unreliable such as intermittent wind power as too is thermal energy from the sun in the winter months. Gasoline, LPG and coal all have to be supplied in containers and lorries making them all prone to periods of short or interrupted supply. Natural gas on the other hand, by the very nature of the way it is transported to customers in a continuous way, is always available.  

To understand how such an intricate natural gas supply network operates it will be helpful to provide an illustrative example from Holland, a major producer, user and exporter of natural gas to adjoining countries.

Although this example refers to Holland, precisely the same types of natural gas transportation infrastructure are used throughout the world to bring natural gas to consumers.

The whole supply system as described above is operated on a 24 hour every day basis. It never stops and is a continuous and seamless operation from the perspective of the natural gas consumer.

High pressure natural gas transmission pipelines can be buried safely underground and constructed quickly once the necessary routes have been surveyed and 'way-leaves' agreed with landowners. To illustrate how rapidly such networks can be constructed in comparison with other type of  energy infrastructure investment, in Holland in 1965 there were only 790 km's of transmission pipelines that had risen to 4588 km's by 1985. In the space of twenty years some 3798 km's of high pressure large diameter underground pipelines had been constructed serving the whole country with natural gas. In contrast, a major coal fired power station can take up to 12 years to be constructed and fully commissioned and nuclear power stations 20 years or longer.  

Natural gas is transported through transmission and distribution pipeline networks at different pressures and volumes. Show below is a diagram that describes the different transportation stages of natural gas from the producer through to the end user.