Figures 2.12b AnD 2.12c Show the arrangement of natural and forced circulation HRSGs. In the natural circulation unit the differential head between the cold water in the downcomer circuit and the hotter, less dense mixture in the riser tubes drives the steam-water mixture through the evaporator tubes. The circula­tion ratio (CR), which is discussed in […]

A once-through HRSG (called an OTSG) does not have a steam drum like a natural or forced circulation unit (Fig. 2.12). An OTSG is simply made up of serpentine coils like an economizer. Because water is converted to steam inside FIgure 2.12 HRSGs with different type of circulation systems: (a) Natural circulation, (b) forced circulation. […]

Heat recovery steam generators are generally categorized according to the type of circulation system used, which could be natural, forced, or once-through as illustrated in Fig. 2.12. Natural circulation units have vertical tubes and horizontal gas flow orientation, whereas the forced circulation HRSG uses horizontal tubes and gases flow in the vertical direction. Once-through units […]

Gas turbine-based combined cycle and cogeneration plants are springing up throughout the world. The advantages of gas turbine plants are discussed in Chapter 1. Though gas turbine exhaust is used to heat industrial heat transfer fluids and gases, the emphasis here will be on steam generation. Gas turbine exhaust is clean; therefore water tube boilers […]

Hydrogen and ammonia are valuable chemicals in various processes. The steam reforming process is widely used to produce hydrogen from fossil fuels such as natural gas, oil, or even coal as shown in Fig. 2.10. There are several variations of the process, but basically the steam reforming process converts a mixture of hydrocarbons and steam […]

Sulfuric acid is an important chemical that is manufactured using the contact process. Heat recovery plays a significant role in this system, whose main objective, is to cool the gas stream to a desired temperature for further processing. Raw sulfur is burned with air in a combustion chamber, generating sulfur dioxide, oxygen, and nitrogen. The […]

A sulfur plant forms an important part of a gas processing system in a refinery. Sulfur is present in natural gas as hydrogen sulfide (H2S); it is the by-product of processing natural gas and refining high sulfur crude oils. For process and combustion applications, the sulfur in the natural gas has to be removed. Sulfur […]

Table 2.1 shows a few aspects of fire tube and water tube waste heat boilers. Generally water tube boilers are suitable for large gas flows exceeding millions of pounds per hour and can handle high steam pressures and temperatures. Fire tube boilers are suitable for low steam pressures, generally below 500psig. Table 2.2 shows the […]

Heat recovery boilers, also known as waste heat recovery boilers or heat recovery steam generators (HRSGs), form an inevitable part of chemical plants, refineries, power plants, and process systems. They are classified in several ways, as can be seen in Fig. 2.1, according to the application, the type of boiler used, whether the flue gas […]

Diesel engines are widely used as sources of power when an electrical utility supply is not available. They may be fired on gaseous or liquid fuels. They are mostly employed in low and medium power cogeneration units, typically 50 kW to 10 MW for natural gas firing, 50 kW to 50 MW for diesel, and […]