ROAD TRASPORT OF COMPRESSED GAS.

Natural gas is generally transported by gas pipeline when it is a question of supplying large users, concentrated geographically, or also if distances are quite short (less than 15 km). But when consumption is widely spread geographically over distances ranging from 20 to 200 km and the quantities of an industrial dimension, but not too large - 160 000 to 600 000 m3 per day - there are advantages in transporting the gas in a compressed form -CNG.

Apart from industry, potential gas users in Rwanda, in particular those currently using wood, are of these types :

• tea and coffee factories are scattered at distances between ?? and ?? from Kivu and have total energy needs of between 100 000 and 200 000 Nm3 per day, not including their needs in electricity, which could also be self generated using gas.
  
• brickworks or small energy-dependent businesses are very spread out but often along the roads, with energy needs of between 30 000 and 100 000 Nm3 per day.
  

On the face of it, all the conditions for profitability of transport of CNG by lorry are reunited.

In order to take up a small space, the gas has to be compressed at the high pressure of 200 b, which requires a fairly robust container, usually made of steel or in composites which are more expensive but lighter.

Normally these containers are cylinders piled on a 20 to 30 tonne lorry trailer, cylinders which contain between 3 000 and 7 000 Nm3 of gas at a pressure of 200 b.

Diagram of a haulage vehicle an d its trailer with steel containers group of containers in composite materials

In order to exploit this expensive equipment, particularly containers, in a profitable way, they have to work together, ferrying efficiently, with generally speaking 3 trailers for each hauling vehicle : one trailer being loaded at the gas source, one out on the road and the third delivering the gas to the customer.

Unloading is optimised by grouping 2 or three consumers or by installing an intermediate storage point allowing for speedy discharging of 200 b to 75 b, in a buried wide-diameter pipe, for example.

Since the gas extracted from Kivu with 85% CH4 is at low pressure, it needs to be compressed in a plant near the lake. Profitability of transport is improved if the gas is enriched to 90-95% CH4 by washing and by dehydrating it so as to avoid water corrosion of metal parts. The gas should be odorised when discharged for safety reasons in the event of a leak.

Competitivity of CNG with other types of energy should be good, and even more so if, in addition to the thermic use of the gas (heating, drying etc.) in small scale agribusiness or for construction material, auto-production of electricity was developed or distribution by small networks to community groups or neighbourhoods for domestic purposes like lighting or cooking. Among competing energy sources, wood could stay competitive for a time but it will become rare, higher in price and the object of a probably more and more severe conservation policy for the forest. As for fuel oil, it should stay a lot more expensive for the foreseeable future.

The setting up of a legal framework for the distribution of CNG can be simple and would concern :

• Apparatus under pressure
  
• The transport of CNG and the safety factor, this latter being mitigated by the fact that, natural gas being lighter than air, it escapes vertically if there is a leak. Moreover, there has never been an accident of CNG transport linked to the gas.
  
• Distribution and the safety factor.