Boilers Basic Components (Att. VIII)

ATTACHMENT VIII TO SAIR’s GUIDELINES SOME EQUIPMENT BASIC CONCEPTS Boilers Basic Components CONTENTS PAGE INTRODUCTION………………………………………………………… 2 STEAM SYSTEM ………………………………………………………… 2 BOILER CHARACTERISTICS ………………………………………….. 3 Major Boiler Components …………………………………………………. 11 Miscellaneous Boiler Components ………………………………………... 16 FABRICATION …………………………………………………………… 17 NONDESTRUCTIVE EXAMINATION…………………………………. 22 HYDROSTATIC TESTING………………………………………………. 23 BOILER SAFETY VALVES ……………………………………………... 23 STANDARDS AND CODES……………………………………………….25 GLOSSARY…………………………………………………………………26 INTRODUCTION This section provides an introduction to the steam generating equipment used by Saudi Aramco, including an overview of typical plant steam systems. The types of boilers and boiler components used by Saudi Aramco are described. STEAM SYSTEM OVERVIEW Terminology for the Design and Operations of Boilers A typical steam system, shown in Figure 1, provides thermal energy in the form of steam to a number of consumers. The key elements in this system are the steam generators, the distribution system, and the users. Supply of boiler feedwater (BFW) to the steam generator and recovery of condensate for recycling are also included in the steam system. 1 Boiler 2 Deaerator 3 BFW Pump 4 Continuous Blowdown Facilities 5 Intermittent Blowdown Facilities 6 Pressure Reducing Station 7 Desuperheater 8 Distribution Piping and Valves 9 Condensate Return System SV System Safety Valves FIGURE 1 TYPICAL STEAM SYSTEM - 2 - The steam generator can be either a part of a process unit using waste or surplus heat, or a separate offsite facility burning fuel in a boiler. The fuel can be gas, oil, or coal. Steam can also be generated by recovery of waste heat from the exhaust of a gas turbine. Waste or surplus process heat can come from furnace flue gases, process coolers (heat exchangers), or hot product rundown. The steam distribution network consists of piping and valves that interconnect between the producers and consumers of steam. Steam can be produced and consumed at various pressure levels. These different pressure levels are usually connected via pressure reducing and steam desuperheating stations, so that surpluses of steam at higher pressure levels can be utilized at lower pressure levels. Although not standardized, commonly used steam pressure levels in Saudi Aramco plants range from 60 to 625 psig. Most plants have a high-pressure (HP) level of 600 to 625 psig, plus one or much lower pressure levels. For example, steam pressure levels at Abqaiq are 625 and 60 psig, and at Ras Tanura the steam pressure levels are 600, 225, 150, and 60 psig. These 60- to 225-psig levels are referred to as medium-pressure (MP) levels. Usually there is also a low-pressure (LP) level at 15 psig. The steam system begins with the supply of treated water to a deaerator, where dissolved gases such as oxygen and carbon dioxide are removed prior to introduction of the water into the boiler. These gases are undesirable because of their corrosive attack on metal surfaces. The water is deaerated by heating it to its saturation temperature and then scrubbing it with steam to carry away the dissolved gases. The deaerator operating pressure is normally the same as the LP steam system (15 psig). Boiler feedwater pumps are used to deliver BFW from the deaerator to the boiler steam drum. Two or more pumps are provided to ensure a reliable supply of water to the boiler. Wherever possible, condensed steam from the steam users is collected in a condensate system and returned to the deaerator for recycling. BOILER CHARACTERISTICS Types The three main types of boilers used by Saudi Aramco are water-tube, firetube, and electric. Water-tube boilers are illustrated in Figures 2 through 5. These are the largest and most common boiler types. A firetube boiler is illustrated in Figure 6, and an electric boiler is illustrated in Figure 7. Water-tube boilers have no real pressure or size limitations. The basic configuration is a firebox surrounded by tubes filled with water. Located at the top of the water-tube boiler is a drum in which steam is separated from the water. Water circulates from the steam drum down through the water tubes and back to the steam drum. This usually occurs because of natural circulation, although some boilers have forced circulation systems. The smaller-sized water-tube boilers are usually shop assembled and delivered to the field in a complete unit. These units are referred to as package boilers. The maximum size of package boilers depends largely on transportation limits. Larger units can be shipped in a few modules which are assembled in the field. Many Saudi Aramco boilers are package units, with the largest having a capacity of about 600,000 lb/hr of steam at a design - 3 - pressure of about 880 psig. Typical package boilers are shown in Figures 2 and 3. Larger sized water-tube boilers are field erected. A typical field-erected boiler is shown in Figure 4. FIGURE 2 PACKAGE WATER-TUBE BOILER - 4 - FIGURE 3 WATER-TUBE BOILER - 5 - FIGURE 4 FIELD-ERECTED WATER-TUBE BOILER A gas turbine waste heat boiler is illustrated in Figure 5. These boilers are usually a special design. They can be designed as unfired units operating on waste heat only, or as supplementary fired units, with gas or liquid fuel, to increase steam production. Because of the type of supplementary firing used, the boiler shown in Figure 5 can also be referred to as a duct-fired waste heat boiler. Boiler size is dependent on the size of the gas turbine. They typically produce 100,000 to 400,000 lb/hr of steam at 150 to 600 psig. - 6 - FIGURE 5 GAS TURBINE WASTE HEAT BOILER Firetube boilers are generally of small size (under 100,000 lb/hr and more commonly under 50,000 lb/hr) and low pressure (under 250 psig and more commonly 150 psig or lower). The steam is usually not superheated. The name "firetube" comes from the arrangement where hot combustion products flow inside tubes that are located in a water- filled cylindrical shell. Firetube boilers are less expensive than water-tube boilers of the same size and pressure rating. Firetube boilers are usually packaged and skid mounted. - 7 - FIGURE 6 FIRETUBE BOILER Electric boilers are often used for small steam loads at locations outside of main plants, for example, mechanical shops, dining halls, and hospitals. Electric boilers are usually very small in size (generally less than 25,000 lb/hr) and low pressure (less than 100 psig). In a resistance boiler, electric resistance heating elements are immersed in a water bath that is enclosed in an outer pressure vessel. Heat input and steam output are regulated by controls which select the number of heating elements to be energized. - 8 - FIGURE 7 ELECTRIC STEAM BOILER Figure 8 lists the major boilers in Saudi Aramco plants. - 9 - FIGURE 8 SAUDI ARAMCO BOILERS - 10 -.

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