The switch valves are the most significant valve in the delayed coking unit. Delayed Coking refers to the thermal cracking process in a coke drum converting petroleum residuum to light oil or gas products. With the switch valves, the process would be more efficient and safer.
The demand for refined products expands worldwide nowadays. Hundreds of refineries around the world are transforming crude oil into transportation fuels, heating oil, and other hydrocarbons used to make solvents, plastics, fuels, and other products. Approximately 10% of the crude oil is processed through a delayed coker. In the high-temperature cooking process, switching valves are required to control and operate the units safely.
In a typical 4-drum delayed coker, two coke drums are feeding and processing and the others are being cooled and opened for coke removal. Without control valves, the workers have to manually open the coke drums. It is dangerous since it exposes the workers to high-temperature steam, hot water, and falling coke, which resulted in potential injuries and even fatalities. The installation of switch valves improves the efficiency and the safety of the operator, definitely increasing refinery profitability.
To unhead to coke drums from the bottom with the switching valves, the residuum and other system contaminants can be switched from the bottom of the coke drums to the side-feed. There are different flow patterns and coke bed formations created by side-feed technology today.
Manually operating the top unheading is not only time-consuming but dangerous. Top unheading switch valves are a design seeking to solve this very problem accordingly. Top unheading switch valves connect the top flange of a coke drum and maximize safety in an enclosed system. It can also work with the auto switch boring and cutting tools to eliminate the need for personnel on the cutting desk.
The control valves are used to stop, start or vary the flow of fluids, control the direction of flow, and regulate the downstream pressure. The disc of a valve is the part that is used to open, close or regulate the flow of fluids including oil, water, and so on.
Different types of control valves get their names from the type of discs used. For example, the ball valves have ball-like discs. The globe valve is the exception, it is named after the shape of the valve body. Following is the introduction of gate valve, ball valve, and globe valve.
The gate valve is one of the most common and simplest types of control valves. It is normally used in-line for isolating and controlling the flow of gas within a system. When gate valves are fully opened, there is very little resistance to the flow passing, which means the valves are having a very low pressure drop.
In a rising stem gate valve, the stem of the gate valve passes through the valve, the seat arrangement, and up through the handle wheel. While the valve starts acting, the stem rises out the top of the handwheel, pulling the disc up, then drops down again.
Gate valves are only used for open and close. When the disc travels up half, the flow through the valve is not linear or proportional to the amount that the valve is open. In addition, when the flow of gas passing with the valve half-opened, the turbulence and the high velocity of passing flow result in seat and disc wear and pressure drop.
The ball valve is a rotary motion valve that is fast-acting. Its ball-shaped disc is used to stop or start the flow. When an operator turns the handle to start the flow, the disc rotates to the point where the hole through the ball is in line with the valve inlet and outlet. When the ball valve is shut, the disc rotates so that the disc can be perpendicular to the flow and block it.
Ball valves are fast-acting, relatively cheap, and have low pressure drop. The ball disc also reduces the chance of leakage. However, they are not suitable for flow throttling or high-temperature applications.
Globe Valve is named after the shape of the valve body. Unlike ball valves, globe valves are linear actuated valves, which are slower than rotary valves. It can be used to start, stop and regulate flow. In contrast with the gate valve, the disc of a globes valve travels linearly upwards and downwards, proportionally allowing the flow to pass through. Therefore, it can be used to regulate flow. However, globe valves have relatively high pressure drop, and they are heavier than most other valves with the same flow rate capacity.
There are four different globe valve body designs: Straight-flow, Angle-flow, Cross-flow, and Y-flow. The rising stem can indicate the position of the globe valve disc. To seal off the top of the valve bonnet and close off the packing from the system pressure, the operator can install a backseat onto the disc.
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