Revised and re·issuec on January 1992, HSE (United Kingdom) published HSE Safety Notice 11/90. The appendix of this notice details the design principle of the mud gas separator (Poor Boy Degassers or Gas Busters). Extract the HSE Safety notice detailed as below. For compliance requirement & support, contact Kapwell representative via email call on 01224 966776.

1. Avoid plugging- Mud-gas separators should be able to handle a high proportion of mud solids and may experience hydrate plugging as a result of gas expansion through the choke. Mud-gas separator designs should, therefore, be based only on a liquid seal system matched to an adequate gas vent.

2. Principles of Liquid Seal Design: The liquid seal ensures that separated gas vents safely without breaking through to the mud tanks. The seal may be in the form of an external U-tube or may be based on a dip tube extending into a tank, usually the trip tank. The separator vessel may be vertical or horizontal and fitted with internal baffles and distribution nozzles, but the performance of the liquid seal is independent of these design features.

3. Capacity to Vent Gas- This capacity is the rate at which gs can be vented when the seal is operating at its maximum pressure differential when the liquid seal contains only associated liquids from the hydrocarbon influx. A gradient of 0.3 ps/ft should be assumed to determine the maximum pressure differential.

4. Capacity to Separate Gas from Mud – The capacity to separate must not be confused with the capacity to vent. Ideally, the capacity to separate should be greater than the vent capacity, but this is not possible given the low operating pressure and the constraints of the rig layout. In practice, the capacity to separate may be only 10% of the vent capacity. The capacity to separate is controlled primarily by the gas velocity in the separator above the inlet section. In vertical separators, the area of the separator is the controlling function. Internal baffles will improve the separation process, but care must be taken to avoid increasing the risk of plugging with solids/hydrates.

5. Capacity to Dump Liquids- The size of the liquid outlet line should be based on a minimum gravitational rate from the separator of 6 barrels per minute of 12 PPG mud of average viscosity.

6. Requirement for Pressure Monitor- The performance of a mud-gas separator should be monitored by observing the pressure in the separator. A low range pressure gauge should be installed, readily visible from the choke control position. A remote pressure transmitter may be used for this purpose but should be capable of operation without dependence on rig air supply or rig electrical power where remote gauges are installed. a backup gauge on the separator vessel itself is still recommended.

7. Need for Secondary Vent on U-tube Seal- If the seal is based on a U-tube design, an independent secondary vent pipe. Preferably 6″ nominal diameter or larger, it should be fitted at the highest point of the pipework to avoid siphon effects and as a back-up to dispose of gas carried through the U-tube seal. The secondary vent need not extend to the top of the derrick. It should never be tied into the primary vent.

8. Overboard Lines (Blowdown Lines)- In exceptional circumstances, Well control may require that displacement of the kick continues regardless of the capacity of the mud·gas separator to handle wellbore fluids. All offshore installations should have a means of diverting the flow from the choke manifold through overboard lines and isolating the mud-gas separator. The pressure rating of the piping and valves on overboard lines should not be less than the pressure rating of the buffer vessel of the choke manifold to which they are connected. The lines should be as short and straight as possible.


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