Limited Steam Export

A limited export steam plant is defined as a plant that makes some export steam but significantly less than the maximum. This is typically achieved by adding a combustion air preheat unit (CAP). This unit consists of a modular heat exchanger that heats the combustion air to the SMR by heat exchange with the flue gas from the SMR. The hot combustion air reduces the fuel requirement for the SMR, which in turn reduces the steam production. 

A typical combustion air preheat temperature for this type of plant is approximately 750°F. This permits use of carbon steel ducting in the air preheat distribution system. Table 4 gives a typical feed and utility summary for a limited export steam plant, as defined above. 

Note that the limited export steam plant makes less than half as much export steam as the maximum steam export case, but also uses less natural gas. At the same time, the limited steam export plant capital cost is higher, because of the addition of the air preheat unit. 

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Figure 2. Steam/Methane Reforming with Limited Steam Export...

The steam value and fuel price typically determine which of these two cases is the most economic. A high steam value (relative to fuel price) favors the Maximum Steam Export Case. A high fuel price and a low steam value (relative to fuel price) favor the Limited Steam Export Case. 

When possibilities to export steam or power are limited, part of the secondary reformer waste heat is used, in addition to steam generation, for steam superheating, a feature in common with other modern concepts. Proprietary items in addition to the horizontal converter are the traditional Kellogg reformer, transfer line and secondary reformer arrangement, waste-heat boiler, and unitized chiller in the refrigeration section. 

This section provides a comparison of power reactors built in the UK with the Soviet RBMK. But it is worth recollecting that, elsewhere in the world, other types of power reactors are in use. The most widely built reactor is the Pressurised Water Reactor (PWR) but the second is the Boiling Water Reactor (BWR), a light water reactor in which, like the RBMK, steam is generated in the core and passed to the turbines in a direct cycle. Light (i.e. ordinary) water is used as coolant and moderator. The Canadian industry has developed the CANDU series of reactors, with limited export to India, etc., which have many pressure tubes to retain the coolant, as in the British SCHWR and Soviet RBMK, but are heavy-water-cooled and moderated. 

Table 4. Limited Export Steam Feed and Utility Summary...

No import or export of steam or power across ammonia plant battery limits. 

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