As mentioned in the feature article on pages 68, 69, 70 and 73, geothermal energy has many advantages over other (renewable) energy sources such as a
continuous supply and less land-use. On the other hand, the temperatures and pressures need to be regulated safely to safeguard workers, the environment and equipment in geothermal power stations.
Given the critical conditions, due to deeper drilling and subsequent temperatures and pressures, the API 6A-standard for Wellhead and Christmas Tree
Equipment (also available as ISO 10423) has become the norm in the geothermal sector.
In general, two temperature classes are in effect: the X for temperatures up to 180 degrees Celsius and Y for temperatures up to 345 degrees Celsius.
Choices in terms of materials, pressure classes and function of the wellhead (control) depend heavily on the geological conditions.
Rise of the ball valve
As for the valves used in wellheads, there are roughly two options: either a gate valve or a metal-seated ball valve. It looks that the ball valve has become more and more accepted in the geothermal sector at the expense of gate valves, according to Hartmann Valves.
There are several reasons for the rise of the ball valve in geothermal wellhead design. Ball valves facilitate a double barrier option independent of each other: an extra safety feature.
Gate valves also tend to be prone to scaling, due to dissolved minerals that make their way up to the wellhead and crystallise when temperatures and pressures are decreasing. As these scalings accumulate, this accumulation hinders the proper closing of the gate. Ball valves are better suited to combat the effects of scaling as the inner body is sealed off hermetically. Deposits (due to particle accumulation) on the ball are removed by the edge of the seat ring. As a result, ball valves require less maintenance and repair and generally require less down-time, increasing the capacity of the geothermal power plant.
Double in size in the next ten years
Flexibility in wellhead design for geothermal energy is also a significant factor.
A modular design facilitates easy maintenance, repair-or-replace, for example of the pumps. An eccentric pipe connection enables the use of scaling and corrosion inhibitors and makes room for electrical cables to power pumps etc.
The ability to change from production to injection and vice versa also comes into play in the wellhead’s design. In some cases, this change needs to take place to maintain or even increase process efficiency. This means that all components (actuation, automation, standardised interfaces, etc.) in the wellhead should be interchangeable for both operational functions (injection, extraction).
To conclude, geothermal energy is an attractive (and growing) market that requires experienced and flexible suppliers and high-performance equipment. Hartmann expects this market to double in sales in the next ten years due to projected project development and – in general – an increase in demand for renewable energy.