Capturing Basic Design Data

Boiler design is divided into two phases:

1. Process and basic engineering consisting of

A. Thermal design for sizing of all HSs, auxiliaries, and P&I schemes

B. Firing equipment design and integration with the main boiler

C. Layout design of total boiler plant and PPs

D. Electrical and instrumentation engineering as per scope

2. Detailed engineering and drafting mainly consisting of

A. PP design dealing with all PPs and integral piping

[2] Specific gravity

• The gas analysis or composition is expressed in volumetric terms on dry basis (moisture-free basis).

• Analysis is done by chemical means of absorption, distillation, combustion, infrared spectroscopy, or gas chromatography; the last two methods are the most accurate.

• Calorific value is determined by bomb calorimeter. It is common to denote CV on dry volumetric basis.

• For combustion calculation purposes, weight basis is needed. This is usually calculated from volume using density.

• Specific gravity is compared with the weight of air for the same volume. ASTM D1070 covers three methods.

Fossil Fuels

Natural Gas

Natural gas is perhaps the nearest to the ideal fuel, as it is almost free of ash and has high CV.

• There are no storage facilities required for the fuel.

• There are no dust collection or ash disposal issues.

• The boiler control is extremely simple, sensitive, and seamless.

• The boiler is very compact.

Natural gas is found usually close to oil deposits, compressed in the underground porous rock or shale formations at pressures as high as 150 bar.

• Associated gas. When gas is trapped above oil (which in turn is on top of salty water), it is called associated gas, and it contains heavy HCs.

• Wet gas. When gas is in contact with the oil, it is charged with heavy HCs such as pentane (C5H12) and hexane (C6H14), which are liquid at ordinary temperature and pressure, and this gas is known as wet gas.

[3] Corrosion

Furnace geometry, size and design, location of soot blowers (SBs), spacing of tubes in convection passes, and other parameters are all governed by ash properties. In fact, coal — fired boiler design substantially revolves around the management of ash. The behavior of ash in a boiler at various temperatures and locations can be predicted from the following properties in a reasonably accurate manner.

[4] High alumina

[5] Plastic refractories

2. Ramming mixes

3. Gun mixes

4. Castables

[6] Draft plant items:

A. Flues, ducts, hoppers, and casing

B. Dampers

C. Expansion joints

D. Airflow-measuring devices

Draft plant equipment is a boiler auxiliary and discussed in detail in Chapter 8. Draft plant items are fabricated parts, which are discussed in the following sections.

[7] Based on density

Horsepower and static pressure are proportional to gas density at constant speed

[8] Pulse jet filters (PJFs)

In RGF and SF, where the bags are open at the bottom and closed at the top, the dusty gases enter from the bottom and the dust is collected on the inside of the bags. Mechanical shaking used for removal of dust imposes severe stresses on the bags. Bag materials currently available cannot withstand such violent stresses for a large number of cycles. SFs have short lives and are not popular. RGFs are, by far, the most popular design, as

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