When thermal energy is applied to furnace tubes, the process of boiling is initiated. However, the fluid leaving the furnace tubes and going back to the steam drum is not 100% steam but is a mixture of water and steam. The ratio of the mixture flow to steam generated is known as the circulation ratio, […]

Fin tip temperatures in boilers of membrane wall design depend on several factors such as cleanliness of the water or tube-side fouling, fin geometry, and heat flux, which is a function of the load and gas temperature. Assuming that membranes are longitudinal fins heated from one side, the following equation may be used to determine […]

The energy transferred to the furnace is obtained from the equation Q = — T4) = Wf LHV — Wghe ^ ^ heat 1lux Figure 3.11 Relating fin tip temperature to heat flux in membrane wall furnace. FIgure 3.12 Furnace outlet temperature for gas and oil firing. Where Q = energy transferred to the furnace, […]

The furnace is considered the heart of the boiler. Both combustion and heat transfer to the boiling water occur here, so it should be carefully designed. If not, several problems may result, such as lower or higher steam temperature if a Table 3.3 Boiler Performance at Low and High Steam Pressure3 Low pressure High pressure […]

Another example of custom designing is shown in Example 3. In this example, we are asked to design a boiler for a lower pressure of operation for the first few years with the idea of operating at a higher steam pressure after that. Example 3 An interesting requirement was placed on the design of a […]

Example 2 This example illustrates the point that surface areas can be misleading. A boiler generates 100,000 lb/h of saturated steam at 300 psig. Feedwater is at 230°F, and blowdown is 2%. Standard natural gas at 10% excess air is fired. Boiler duty = 100.8 MM Btu/h, efficiency = 84.3% HHV, furnace backpressure = 7 […]

Custom-designed boilers, as the term implies, are designed from scratch. Based on discussions with the burner supplier and the level of NOx and CO desired, one first selects the type of burner to be used and the emission control strategy. A few options could be considered: Use a large amount of flue gas recirculation (FGR) […]

Water-cooled furnaces have a number of advantages over other types: 1. The front, rear, and side walls are completely water-cooled and are of membrane construction, resulting in a leakproof enclosure for the flame, as shown in Fig. 3.2. The entire furnace expands and contracts uniformly, thus avoiding casing expansion problems. When refractory is used on […]

Standard boilers, which are pre-engineered packages, are inexpensive and are used in applications that are not very demanding in terms of process or emission limits. Decades ago, various manufacturers had developed so-called standard designs for boilers of 40,000-200,000 lb/h capacity with fixed dimensions of furnace, tubes, tube spacing, lengths, and surface areas. If someone wanted […]

Packaged boilers are widely used in cogeneration and even in combined cycle plants as auxiliary boilers providing steam for turbine sealing and steam for other uses when the gas turbine trips and the HRSG is not in operation. These boilers are generally shop-assembled and custom-designed. Typically, boilers of up to 250,000 lb/h capacity can be […]