KenGen pioneers wellhead power generation systems

By John Oyuke

KenGen will pioneer a new technology in geothermal power generation, when it installs the first wellhead generator unit at Olkaria next month.

The technology involves tapping steam from wells, which are undergoing tests, or are awaiting connection to permanent plants to benefit from early generation.

The move by the electric power generator comes at a time the country needs an estimated Sh78.54 billion in the next three years to tap its geothermal power potential, and avoid over-reliance on the erratic hydroelectric power.

Long drought has slashed the capacity of main dams, forcing shutdowns and leading to reliance on costly diesel-powered generators, which in turn have pushed up energy bills.

George Muga, project engineer, says KenGen expects the first pilot unit to be up and running early of next month, delivering about 5 megawatts.

Thereafter, more units with an expected yield of 70 megawatts are expected to be in place by April next year.

"When this comes on line, the wellhead units will be moved to other geothermal areas like Menengai, and Longonot," he says.

A permanent power plant takes between 24 to 36 months to construct and commission.

Muga says through the move, KenGen would step away from traditional methods and use wellhead generators to achieve the same results, the first company to do so in Africa.

Drilling of geothermal wells takes between 50 to 70 days at depths of between 1.8 and 2.8km.

After this, the well is put under discharge test to determine its flow characteristics and establish the power output at different wellhead pressures.

The current method is to pass the geothermal fluid through a pipe, measure the total flow and direct the fluid to a wellhead separator to separate the steam from the water.

New technology

The water fraction is measured and the difference between the total mass flow and the water gives the steam fraction.

However, Muga says it has been found normal well testing wastes resources. In most cases, wells are discharged over long periods to assess their response to exploitation as the resource is drawn down without tangible production.

"Through use of the new technology, KenGen will test the wells while routing the steam through the generators, which will supply power to the grid," he says.

Using this approach, Muga says, the country’s energy demand is achieved within as short a time as 70 days of commencing well drilling.

"It is no longer economical to drill all the wells needed to supply a permanent power station before financing is sought or returns are realised from the wells," he says.

According to Muga, power from the first well can be used to supply the next well to be drilled, thus reducing diesel usage at the rigs, and the balance sent to the grid.

Each well once completed starts contributing to the grid and could as well be doing this for the next four to six years it takes to complete all wells and build the main power plant.

In essence, Muga noted, geothermal wellhead generators achieve environmental friendliness, and early generation of power using renewable resource and provide an early revenue stream that can be used to drill more wells or contribute to financing of the main power plant.

Change of ecosystem

He says when using the standard method of well testing as has been done in the past, the discharge of steam into the atmosphere hurts the environment because the temperature of the immediate environs is raised above normal conditions and may result in change of the eco-system.

"Use of wellhead generators, however, minimises this effect as the steam will pass through the generators with the steam pressure and temperature dropping and ultimately condensed to a liquid, forming a closed loop with very little or no atmospheric venting."

Energy Minister Kiraitu Murungi says the country needs to ramp up power production to meet growing demand.

"To address the current supply-demand imbalances and provide reserve margin of at least 20 per cent, we need close to 1,800 MW in new generation capacity," Kiraitu said last year.

The country is currently seeking to expand generation of electricity from other renewable sources, including a 300 MW wind farm in North Eastern Province due to be commissioned by 2012.

The country has spent Sh630 million dry areas on solar power for hospitals, schools and health centres in the last four years and has set aside another Sh500 million more in the 2009/10 budget.