Compressed Natural Gas for Power Generation in Nigeria

By Abimbola Shode

The erratic nature of electricity supplyfrom the Power Holding Company of Nigeria (PHCN)has created the need for industrial and large scale consumers of electricity to resort to self-generation, utilizing natural gas or liquid fuels, to augment power supply. Natural gas is composed mainly of methane (CH4)and has some attractive properties – it is a cleaner, safer, cheaper and more reliable alternative to conventional fuels like diesel, petrol and LPFO, especially for industrial and commercial users. 

Compressed Natural Gas (“CNG”) is made by compressing natural gas to less than 1% of the volume it occupies at standard atmospheric pressure. CNG can be stored in steel or composite containers at a pressure of 200–248 bar (2900–3600 psi), usually in cylindrical vessels for storage and transportation over short/medium distances (10km to 100km on average). 
Why CNG for power-generation? 

CNG provides a platform for meeting the gas supply needsof a captive power plant utilizing natural gaswhere the cost of connecting to a pipeline network is not economical. This may be based on the customers’ volume requirements or the distance from the gas pipeline grid. 

CNG Value Chain 

CNG is produced from natural gas. The typical value chain of processes that underlie the conversion of pipeline natural gas to CNG is shown below: 

1. Sourcing of natural gas from the pipeline - A new spur line is constructed to connect the CNG plant location to the existing gas pipeline via the shortest route. 

2. Mother Station - Natural gas supply (post filtration and metering) is then fed into dryers to remove any form of moisture from it. The gas is thereafter fed to the compressor. The compressor serves mainly to increase the pressure from the pipeline pressure to the desired pressure for CNG, in this case from 7-19 barg to 200-300barg). 

3. Transportation and Storage - After the compression, the compressed gas is ready for dispensing directly to the tube trailers for transfer to the customers. When no trailers are available to load, the compressed gas shall be stored in steel cylinders, arranged in crates. These crates can be loaded directly on trailers subsequently.These trailers are then attached to truck-heads and driven to customer locations. 

4. Gas fired power plant - Upon arrival at the customer location, the CNG trailer will be attached to a pressure reduction and metering station where the pressure would be reduced before it is then fed to the Gas fired plant for power generation. 

Figure 3: CNG value chain 

Power Generation using Natural Gas 

Power generation using natural gas can be done with gas turbines or gas engines. Gas engines are preferred to gas turbines for smaller scale captive power generation because they are less expensive and more efficient. Gas engines require longer service intervals, maintenance-friendly engine design, and low fuel consumption. 

 Gas turbines are however useful when dealing with power generation on a scale ranging from 11MW and above. Gas turbines offer high reliability, operational flexibility and reduced emissions.For captive power generation; mono-fuel, bi-fuelor multi-fuel engine configurations are recommended depending on the requirements of the user. 

Mono-Fuel Engine 

The mono-fuel engine uses natural gas as its only fuel source. It is therefore able to be optimized for natural gas operation and the lowest emission results.The reduced wear and tear and reduction in maintenance and fuel costs are most significant with mono-fuel engine configurations. The major disadvantage of this engine configuration however is there is no provision for back-up in event of gas outages. There is also the added comfort of dealing with only one type of fuel. 

GE Jenbacher 320 GS – 1,063KW (Single-fuel) 

Bi-Fuel Engine

Bi-fuel natural gas engines are designed to run on a mixture of natural gas and a liquid fuel. The primary fuel is natural gas but they are designed to operate with the liquid fuel as a ‘pilot’ ignition source. These engines can also operate on 100% liquid fuel but not on 100% natural gas. The major advantage of having bi-fuel engine configuration is the ability to switch to a liquid fuel in the event of gas outages. 

GE Jenbacher 320 GS – 1,063KW (Single-fuel) 

Multi-Fuel Engine

Multi-fuel engine configuration involves the use of an engine that can run on gas and at least two other liquid fuels such as LPFO and Diesel. For any captive power solution, a multi-engine configuration is preferred to allow for load management, optimization of fuel consumption and protection against total shutdown in the event of the failure of an engine. Multiple engines running can be synchronized to give the desired output. A multi-engine configuration also makes scaling up easier when demand increases. Furthermore, both engine types can be used for cogeneration, which involves capturing waste heat for use in heating or cooling purposes. Cogeneration enhances efficiency and hence leads to increased savings on fuel costs. 

Gas Network Services Limited 

Gas Network Services Limited, a subsidiary of Oando Gas & Power Limited is developing a Compressed Natural Gas (CNG) Mother-station (CMS). The facility will have an initial capacity of 150mmscm/d and be constructed on land acquired at Ilasamaja in the Isolo area of Lagos State. The facility is expected to commence operations in Q4 2012. The CMS will feed tube trailers for re-distribution to prospective captive power off-takers 

How do I get CNG for Power Generation? 

- Provide and prepare site for CNG storage (Jumbo trailers) 

- Construct internal piping for CNG delivery and off-take 

- Negotiate and Agree Commercial Terms (Natural Gas Sale and Purchase Agreement). 

- Execute Agreement 

- Project Execution and Delivery 

Contact Persons 

Should you require further clarifications on CNG for power generation, please feel free to contact: 

Abimbola Shode 

Tel: 0809 709 9504 

Email: ashode@oandoplc.com