South African company completes EPC for Mozambique gas plant

29th January 2016

  

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South Africa-based oil and gas equipment supplier Energas Technologies, in the fourth quarter of last year, completed the engineering, procurement and construction (EPC) for Mozambique-based gas power station Gigawatt Mozambique’s high pressure reduction and metering station (HPCMS).

“Pressure reduction and metering stations are often situated in remote locations with no or unreliable electricity supply or communication infrastructure. Equipment used in such stations is, therefore, required to be highly reliable and safe, with minimum maintenance requirements,” says Energas Technologies MD Hendrik van Huyssteen.

The gas for the power station is supplied from the Temane gasfield through a 500 km high-pressure pipeline with designed pressure of 125 bar. However, the gas is required at a pressure of 6 bar and a temperature above the dew point.

Therefore, pilot-operated regulators and slam-shut valves process solution providers Honeywell’s Gorter product line that are predominantly used. These regulators can accurately regulate pressure from 125 bar down to 6 bar in one stage and with low noise levels, notes the company.

As a result, high safety integrity levels are required for pressure reduction stations, owing to the possible risks of explosions should the regulating system fail. Therefore, the design standard for gas stations in South Africa is American Society of Mechanical Engineers B31.8, which has specific mandatory requirements to protect users.

Two regulators are used in series to comply with the standards, one of which is a controlling regulator and the other a monitoring regulator in a fully open position.

“The operating regulator is designed to open if it fails, at which point the monitoring regulator will instantly assume control. A second level of over‐pressure protection is provided in the form of Class 900 slam-shut valves,” explains Van Huyssteen.

In this instance, HPCMS skid‐mounted gas‐fired hot water heaters were supplied to Gigawatt Mozambique. These heaters, with a capacity of more than 1 MW each, were built on skids in South Africa and then transported to site.

The electrical energy produced by Gigawatt Mozambique will be exported to the Electricidade de Mozambique transmission grid through a 275 kV bus bar connected to the recently built Ressano Garcia substation.

Once completed, the plant will consist of an engine-hall, housing 13 natural gas‐fired internal combustion engines manufactured by designers and manufacturers of integrated power systems Rolls- Royce in Bergen, Norway, and associated motor and generator suppliers ABB.

Metering and Monitoring

Meters for billing are incorporated into the pressure reduction station. Ultrasonic meters are used for the mainline billing, while positive displacement meters are used for lower pressures.

“Besides being extremely accurate, ultrasonic meters have the advantage of having no moving parts and so they require no maintenance. As gas pressure and temperatures vary all the time, volume correctors are used to calculate the gas volume to a standard base pressure and temperature for billing purposes,” says Van Huyssteen.

He adds that metering standards are mostly based on the American Gas Association standard AGA-8. Where stations are in remote locations, clients usually require remote metering systems to read the meters from a control or supervisory station. Technologies available are cellphone networks, satellite communications or fibre-optic lines.

In addition to taking meter readings, clients also need to monitor the status of the station and control the emergency shutdown valve on the inlet of the station. In- and outlet gas pressure and temperature, and filter differential pressures are typically monitored.

Energas notes that, at a time of local energy crisis, it is imperative that it actively seeks out feasible power supply options. Natural gas is both feasible and viable in answering to this need and is increasingly used for power generation and industrial plants – but constant supply is crucial.

“With the expertise to serve all spheres of the oil and gas industries, Energas Technologies is well‐equipped to provide advanced monitoring and control technologies for a smooth and consistent energy supply – with no interruptions,” concludes Van Huyssteen.

Edited by Zandile Mavuso
Creamer Media Senior Deputy Editor: Features

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