header image of digging in the dirt bitumen or biodiversity

Digging in the dirt - Bitumen or biodiversity: A false dichotomy

Gobind Khiani - 15 September 2016

This is the fourth part of the series of articles on the topic of oil sands.

About the author

Mr Gobind Khiani
Gobind Khiani P.Eng. (AB, BC, SK) is a Valve World columnist and Lead Discipline Engineer at Fluor Corporation, Canada.
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Oilsands projects are a giant environmental clean up project as Canada takes the dirty, oil saturated sand from earth and rivers, further washes it and reverts it as green producers.

Fossil fuel has been always an environmental concern on the impact of the exploration of oilsands on biodiversity. The Media have always presented the issue to the public in such a way that makes it seem as if we can either have oil exploration or protection of the environment by alternative energy sources. Warnings about massive and irreversible impacts on biodiversity are given, but these arguments are misleading to the general public. While there are risks, there are also solutions to minimize, mitigate or completely reduce any hazards.

the weather condition in canada can be tough
The weather conditions in Alberta can be tough.

Also environmentalists have concerns over the water used by the oilsands industry, over the amount of water they are allowed to draw from rivers.

However, the historical data for the industry’s water usage reveals that withdrawals from rivers for surface mining represent only a very small percentage of river flows and in-situ projects (SAGD, CSS) do not use any water from rivers.

Further in this article we will discuss Pressure Seal Valves and the benefits of those used in SAGD and CSS technologies:
In the tough and high pressure, high temperature valve applications, pressure seal gate, globe and check valves provide a safe, leak free, pressure-containing valve. The main difference between a bolted bonnet and pressure seal valve is the body/bonnet connection configuration. The pressure seal design bonnet use stake-up bolts to pull the bonnet up and seal against the pressure seal gasket, which creates a seal between the gasket and the inner diameter of the valve body and a segmented thrust ring maintains the load. The higher the pressure the better the seal in a pressure seal valve, i.e. the higher the pressure the more the leakage through the body/bonnet joint is decreased/eliminated. This design has advantages over bolted bonnet valve design mainly in steam, feed water, by pass and higher pressure sealing safety and integrity requirements.

Pressure seal gaskets

One of the primary components involved in sealing the pressure seal valve is the gasket. When the pressure seal valve was invented the pressure seal gaskets were manufactured from iron or soft steel. These gaskets were subsequently silver-plated to take advantage of the softer plating material’s ability to provide a tighter seal. The constant load on the gasket minimized the potential for leakage and the iron/soft steel, silver- plated pressure seal gasket was replaced with one made of die-formed graphite.

During SAGD operations, due to weather cycles in Canadian oilsands – Things to take care of on pressure seal valves

Like thermal binding, the phenomena of center cavity over-pressurization and pressure locking can result in an inability to stroke the valve. The potential of these concerns must be carefully evaluated and addressed in the design phase of the project. ASME B16.34 and MSS-SP-144 state that it is the user’s responsibility to determine the potential for, and provide a means to protect against, Center cavity over-pressurization and pressure locking.

The closure element of double-seated valves (wedge gates, parallel slide gates) may become locked in place by either a buildup of pressure in the center cavity or an increase in the differential pressure upstream, downstream, or both of the seats in a closed valve as a function of decreased line pressure (pressure locking). Fluid trapped in the center cavity at ambient temperatures will expand when heat is introduced (e.g., during startup) and, depending on the fluid type and temperature, this could reach a pressure where insufficient torque is available (manually or actuated) to overcome the pressure and open the valve.

Pressure locking occurs in double-seated valves where the line pressure drops (during plant operation or through accident) on either the upstream, downstream, or both sides of the valve seats, creating a sufficient differential pressure to preclude opening the valve. As in thermal binding, there are several methods to guard against center cavity over-pressurization and pressure locking.

These include the following:

  • Pressure relief hole drilled through the “pressure side” of the body or wedge/ disc half into the valve’s center cavity, thus relieving overpressure to that pressure side. This effectively makes the valve unidirectional in its sealing capability.
  • A pressure equalizing pipe, drilled and tapped from the center cavity to the valve’s “pressure side” bore. When a bypass valve sealing is maintained, when the bypass valve is closed, center cavity pressure is not being relieved.
  • A pressure relief valve that is connected to a pipe drilled and tapped into the valve’s center cavity. This method maintains the valve’s bidirectional sealing capability.
  • A drain valve that is connected to a pipe drilled and tapped into the valve’s center cavity. When the drain valve is closed, center cavity pressure is not being relieved.
  • Bypass with one or more bypass valves and an equalizing pipe joining the center cavity of the valve with the bypass pipe. Depending on the number and configuration of the bypass valves, bi-directional sealing may be maintained.
  • A bypass valve that changes sealing direction as does system pressure. Bi-directional sealing is maintained. Pressure Seal Valves are termed as simple design tougher application valves in SAGD application/s in Alberta.

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