KenGen's Wellhead Technology

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KenGen has pioneered a new technology in geothermal  power generation  by installing two wellhead  generator units at Olkaria and Eburru. The wellhead units generate 5MW and 2.5MW of electricity respectively.

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

This move by KenGen comes at a time the country is experiencing an increased demand for electricity. Rapid Economic growth  and industrialization has created  the need  to accelerate  the drilling  of geothermal wells  in order  to tap geothermal power potential and avoid over-reliance on the erratic hydroelectric power.

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

With the success  of the Olkaria  and Eburru  wellhead  power generating  units, KenGen now intends  to install more units with an expected yield of70MW.Other geothermal areas targeted for this new technology include; Menengai, and Longonot.

Through this move, KenGen has gone on record as the first company in Africa to embrace this new technology and therefore moved a step away from traditional methods to achieve the same results.

Permanent power plants take between 24 to 36 months to construct and commission.  The well head power plant on the other hand takes 6 months hence a quick return on investment

The planning of geothermal development comprises the following stages:

a)   Review of existing information of a prospect

b)   Detailed surface exploration

c)   Exploration drilling and well testing

d)    Appraisal drilling and well testing;

e)   Feasibility studies

f)    Production drilling, power plant design and environmental impact assessment

 

g)   Power station construction and commissioning

h)   Reservoir management and further development

i)     Shutdown and abandonment

The development program from Project identification to Power station commissioning is about 8 years but can be reduced to 5 years if finances are readily available. From the experience of development at Olkaria, it has been learnt that:

Timely financing of the projects is very critical;

  1. Some of  the exploration wells could  have been  used  to run pilot  plants  to generate  some  power  while decisions for further development were being considered;
  2. Staged development has an advantage of making early use of the existing wells thus reducing early expenditure and producing revenue to take the project forward and build confidence in the resource.
  3. Appraisal drilling should not be stepped out too far apart from the discovery exploration  well. Such step-out wells might destroy confidence in the prospect by being unproductive. Planning for competent staff is a very critical, yet often ignored, aspect of a good geothermal development strategy.

Drilling Logistics

  • Drilling of geothermal wells takes between 50 to 70 days at depths of between 1.8 and 3.0km.
  • After drilling, the exploration wells are fully tested. Permeability tests are conducted soon after capping the well.
  • A suite of down-hole temperature and pressure measurements follow this when the well is heating up from the cooling experienced during drilling.

Good wells recover quickly and within one month they develop enough wellhead pressure to discharge on their own. Other wells may require to be assisted to start discharge by compressing and releasing several times. Discharge tests takes a minimum of three months and a maximum of 1 year to determine the full characteristic and long-term behaviour of the well.

During discharge tests, steam and brine measurements are made to determine the amount of steam available. Chemical analysis data of steam and brine is useful during exploitation and also for defining the reservoir characteristics.

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

Normal well testing in its entirety 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.

KenGen Pioneers Wellhead Power Generation Systems

Through use of this new technology, KenGen will test the wells while routing the steam through the generators, which will supply power to the grid.  Using  this  approach  the  country's energy  demand  will  be  achieved  within  as short  a time as  70  days  of commencing well drilling.

Eburru is located approximately 2 hours outside of the capital, Nairobi, in Kenya's Great Rift Valley. The Eburru geothermal field is on the flanks of the OlDoinyo Eburru Volcano and is situated 11 km northwest of Lake Naivasha."

The project  is unique  because, for  the first time,  KenGen  engineers  carried  out  implementation work  without  the assistance  of external consultants. Civicon served as the General Contractor, responsible for construction of the plant.

During the month of January 2015, GDA engineers worked closely with KenGen engineers and operators and Civicon construction crews to complete the commissioning and performance testing.  The plant was first synchronized to  the grid  on  January  23rd. The performance testing was completed just six days later on January 29th.

GDA designed the plant and the steam field, and supplied all of the major equipment. This included an Elliott GYR steam turbine, Kato generator, Lufkin gearbox, Graham condenser and vacuum pump, Goulds cooling water pumps, and a Cooling Tower Depot single-cell fiberglass tower. GDA also manufactured auxiliary equipment in-house to minimize installation time, including the lube oil system, turbine  control valve  assembly,  compressed  air system,  fire pump  skid,  emergency power  system,  and plant control system. The equipment and materials were shipped from the US to Kenya in 11 shipping containers one month ahead of schedule.

 Olkaria 4.7MW power plant

KenGen has partnered with the Green Energy Group (GEG) in constructing the 5MW  Olkaria  geothermal  wellhead  power plant. The  highly  experienced  executive  team  at  GEG  has assembled  a team  commanding a wealth  of  experience  within  the design, engineering, project management and operation  of geothermal  plants and is supported  by a Board of Directors  drawn  from both investment banking and the engineering sector.

This technology has proved sustainable and KenGen has now commanded the lead into the next phase of power generation in line with the country's vision 2030. It has indeed  embarked  on an  ambitious  70MWe  project,  which  has  already  kicked  off  at the Olkaria Geothermal field with the second wellhead plant at 75% completion.  This project will be guided by construction of sixteen wellhead power plants. It is notable that this is the first project of its kind in the world.

Below are photos showing the characteristic long steam lines associated with the conventional power station.

Long steam lines are characteristic of the conventional power plant unlike the case of the portable wellhead power plant.

Power Station Construction and Commissioning

A 50 – 70  MW geothermal  power plant takes about 2 years to construct  and commission. Remember that two years is the time for construction of the power plant only. On average at the figure of 5mw per well, we would require approximately 14 drilled wells each drilled for 3months therefore 52 months in total i.e. about 4 1/2yrs. This means that it will roughly take eight years to have the plant up and running considering delays in procurement.

The construction of the power plant includes;

  • Steam gathering and brine re·injection  system;
  • Power house, electromechanical equipment, cooling towers and blow-down re-injection system;
  • Substations and transmission line; and
  • Commissioning.

Transmission lines can be an issue particularly if the wayleave acquisition is not handled in good time and professionally.  This is because transmission lines can be fairly long and traverse very many land ownerships. Land compensation may be required in some parts while in others outright purchase may be the solution. Power lines, just like power stations require an environmental impact assessment to be conducted.