Effect of reducing the hot water bypass on circulating water consumption
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In many refineries, thermal bypasses are used for controlling the pressure at the top of towers, such as in gas fractionation propylene towers and catalytic stabilization towers. The consumption of circulating water is one of the energy costs associated with these facilities. When the OP of the thermal bypass at the tower top is high, the cooling area of the tubes in the tower top cooler is not utilized fully; some of the tubes remain in a non-cooled state. If the control valve for the thermal bypass is reduced, the cooling area available for the gases increases. To maintain the tower pressure constant, could the amount of circulating water used be reduced appropriately?
Thermal bypass allows for automatic on/off adjustments to maintain stable pressure in the stabilizer tower. If you focus only on the cooling area, what about the efficiency of condensation? Moreover, the stabilizer tower does not always require a large amount of cooling capacity. By manually reducing the thermal bypass to increase the cooling area, even if you reduce the amount of water used in circulation, it will not help maintain the pressure in the stabilizer tower. With automatic control mechanisms in place, there is no need for manual adjustments; I’m sure the frequent need to make adjustments will eventually become annoying as well~~~~
First, it is necessary to understand this control scheme. Keywords: top of tower reflux and product tank, non-condensable gas (the gaseous phase coming out of the top of tower reflux and product tank), oil and gas at the top of the tower (the oil and gas coming out of the top of the tower, which enters the top of tower reflux and product tank after being cooled by condensation). Controlling the pressure at the top of the tower is achieved by regulating the pressure in the top of tower reflux and product tank. When the pressure in the reflux tank is high, the control valve on the non-condensable gas line is opened first, followed by closing the bypass valve on the condenser; when the pressure in the reflux tank is low, the bypass valve on the condenser is opened first, followed by closing the control valve on the non-condensable gas line. This control is carried out automatically. Since the inlet of the cooling medium to the top of tower condenser is in gaseous form (if it has not been heated through heat exchange before entering), and the outlet is in a two-phase state (gas and liquid), the implementation of this control scheme relies mainly on adjusting the amount of cooling medium – that is, the oil and gas from the top of the tower. Therefore, there is no need for manual adjustment of the circulation water volume; it’s merely a matter of adjusting the temperature of the returning hot water. The original poster is worrying needlessly!!!! :)
The poster wants to reduce the amount of circulating water used and thus lower energy consumption. As mentioned on page 272 of \"Questions and Answers on Catalytic Cracking Technology,\" some countries use flow control of circulating cooling water to regulate tower pressure. The advantages of this approach are that the pressure in the tower and that in the reflux tank are roughly equal, the reflux rate remains very stable, the tower pressure is also stable, water consumption is low, and the temperature at the top of the tower should not exceed 70 degrees; moreover, the water needs to stay in the condenser for a short period of time
There’s no need. For smooth operation, it’s better not to change too many things.