Steam Generation And Distribution

Steam for refinery use can be generated from one or more of these following sources: fired steam or unfired steam generators, turbine exhaust or extraction. Figure 10-7 shows the general design principles for establishing refinery steam systems. The steam system consists of steam generators and a distribution network at different pressure levels for process and utility requirements.

The feed is a mixture of condensate and de-mineralized water which is deaerated before being fed to the boilers. The product is high-pressure steam, typically at 900 psig, depending on the end use of the steam. Many process units, such as hydrogen and sulfur plants, have waste heat boilers; and these also generate high-pressure steam. Only boiler feedwater is supplied to these unfired steam generators. The product HP (900 psig) steam is sent to an HP steam header.

Steam System Refinery

CONDENSATE

Figure 10-7. Refinery steam system. BFW = boiler feedwater.

CONDENSATE

Figure 10-7. Refinery steam system. BFW = boiler feedwater.

Typically four types of headers are used for steam distribution in a refinery. In refineries with in-house power generation (Figure 10-8), steam is generated at a higher pressure of approximately 1450psig instead of 900psig, which increases the efficiency of power generation and thus lowers per unit cost of power produced. The four headers are as follows:

1. 900psig. Steam is supplied to the 900psig header from the boiler plant. Some process units, such as hydrogen and sulfur plants, have waste heat boilers that also generate steam at 900 psig. The 900 psig steam is consumed by steam turbines to drive recycle compressors, charge pumps, and the like for many hydroprocessing units of the refinery and as makeup to 475-psig header through a reducing or desuperheating station.

2. 475psig. Sources of 475 psig steam are the exhaust steam of turbines and makeup from the 900 psig steam header. The 475 psig steam is consumed in steam turbines, reboilers, and certain process plants, such as hydrogen. All excess 475 psig steam is reduced and desuperheated to a 150 psig header.

3. 150psig. Sources of 150 psig steam are steam turbine exhaust, waste heat boilers in the process units, and makeup from 475 psig steam. The consumers are process stripping, reboilers, and steam tracing. All excess 150 psig steam is reduced and desuperheated to 50 psig steam header.

STEAM TURBINE GENERATOR SETS

STEAM TURBINE GENERATOR SETS

STEAM TURBINE GENERATOR SETS

ELECTRIC POWER FROM OUTSIDE REFINERY

TRANSFORMER SWITCH GEAR

Figure 10-8. Refinery electrical system.

4. 50psig. Sources of 50 psig steam are steam turbine exhaust, waste heat boilers in certain process plants (sulfur plant condensers), boiler plant FD fans, and from 150 psig steam reduction and desu-perheating. The 50 psig steam is consumed for process steam stripping, reboilers, and steam tracing. All excess 50 psig steam is condensed and returned to the reboiler feedwater.

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