Fire tube design

In a fire-tube boiler, the inlet tube sheet and the tube sheet welds are exposed to the extreme temperature of the reformed gas, which creates rather large temperature gradients and therefore high expansive stress. A positive feature of the fire-tube design, however, is that debris in feed water (mainly magnetite particles spalling from the water-side surface of the tubes) can collect at the bottom of the horizontally-mounted... 

After the cyclone, the gas produced flows to a gas cooler and a hot gas filter. The gas cooler is of a fire tube design and cools the gas to a temperature of 350 - 400 C. After cooling the gas enters the candle filter vessel where the particulate clean-up occurs. Ash is discharged from the candle filter, as well as from the bottom of the gasifier, and is in the meantime cooled and depressurised. 

Flash separator pressure = 500 kPaG Separator retention time = 20 min Approach to equilibrium temperature = 4°C TEG recirculation rate = 0.025 m /kg water removed Contactor internals = bubble cup with 610-mm spacing Rich-glycol outlet temperature = 150°C (from glycol/glycol exchanger) Heat flux for fire tube design = 90,000 kJ/Cm h)... 

Furnaces of this type, such as the steam locomotive furnace—boHet design, had the obvious disadvantage that pressure was limited to ca 1 MPa (150 psi). The development of seamless, thick-waH tubing for stationary power plants (ie, water-tube furnaces) and other engines for motive power, such as diesel—electric, has in many cases ecHpsed the fire-tube boHet. For appHcations calling for moderate amounts of lower pressure steam, however, the modern fire-tube boHet continues to be the indicated choice (5). 

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

In the vei tical-tube single-row double-fired heater, a single row of vertical tubes is arrayed along the center plane of the radiant section that is fired from both sides. Usually this type of heater has an overhead horizontal convec tion bank. Although it is the most expensive of the fired heater designs, it provides the most uniform heat transfer to the tubes. Duties are 21 to 132 GJ/h (20 to 125 10 Btu/h) per cell (twin-cell designs are not unusual). 

The hazard tree also helps identify protection devices to include in equipment design that may minimize the possibility that a source will develop into a condition. Examples would be flame arrestors and stack arrestors on fire tubes to prevent flash back and exhaust sparks, gas detectors to sense the presence of a fuel in a confined space, and fire... 

Fire tube boiler designs employ the upper internal portion of the boiler vessel as a compartment to hold the generated steam, while WT boilers... 

There are four fundamental types of boiler available today—electric boilers, fire tube (shell or FT) boilers, water tube (WT) boilers, and nuclear reactor boilers. Electric boilers apart, all other types are essentially developments from shell and tube heat-exchanger designs. 

Fire tube boilers (shell boilers or shell and tube boilers) convert heat from burning fuel within a furnace (combustion chamber, firebox, or furnace tube) to generate either HW or steam. Fire tube boilers are designed to direct the combustion gases through tubes (held within tube sheets) that are surrounded by BW, thus providing for a greater heat-transfer surface area and improved efficiency. 

Early vertical boilers were constructed in several different designs, including FT and tubeless, dry-top, and wet-top versions. Typically, however, they were single-pass FT units containing an inner, combined BW and steam shell—through which a number of small fire tubes passed—and an outer combustion chamber. 

The early vertical boilers of dry-top design (steam on one side and hot combustion gases on the other side) were subject to the risk of overheating in any fire tubes located above the waterline, but these boilers could provide relatively dry steam with some degree of superheat. 

Scotch marine boilers (SM boilers) derive their name from the Scottish shipyards that built marine vessels for the British Navy. They were the first design of FT boiler to incorporate both furnace tubes and fire tubes inside the shell and replaced the brick-set boilers that used to burn through the bottoms of ships. The SM boiler was a particularly versatile design and quickly became the boiler of choice for many stationary (land) applications as well as for marine duty. Land-based SM boilers (now commonly called Scotch boilers) were not simply marine boilers adapted for stationary duty but incorporated specific design modifications to meet the requirements of land-based industry. 

FB boilers are similar to SM boiler designs except that, instead of a fully immersed furnace tube, they have a bottom furnace (with a crowned combustion chamber) that sits on a refractory floor. Two-pass fire tubes (smoke tubes) connect the combustion chambers to the gas exit vent (smoke stack). 

Hinchley (1975) discusses the design and operation of waste heat boilers for chemical plant. Both fire tube and water tube boilers are used. A typical arrangement of a water tube boiler on a reformer furnace is shown in Figure 3.12 and a fire tube boiler in Figure 3.13. The application of a waste-heat boiler to recover energy from the reactor exit streams in a nitric acid plant is shown in Figure 3.14. 

Process furnace or direct-fired heater Design type, absorbed heat duty, pressure, tube material, capacity... 

For process liquid and gas stream heating, most designs heat the process stream as it flows through tubes that pass through fireboxes, convection sections, or combustion gas stacks, although a few fire-tube heaters exist. 

Am. Soc. Testing Materials, Philadelphia, A STM Designation E 69-50, Standard Method of Test for Combustible Properties of Treated Wood by the Fire-Tube Apparatus. 

Boilers are available in two basic designs a fire tube, in which water circulates in tubes heated externally by fire and a water tube, in which hot gases from fire pass through the tubes in the boiler. Fire-tube boilers are generally limited in size to approximately 12,000 kg/h (25,000 lb/h) and to about 20 bar (250 psig). Their size and pressure limitations preclude their use in large industrial facilities or in power plants. 

Industrial and utility boilers are broadly classified as fire-tube or water-tube. In fire-tube boilers, the hot combustion gases pass through tubes, and heat is transferred to water outside the tubes. Most steam locomotives had this type of boiler. The most common and least expensive boiler of this type is the horizontal return tubular (HRT) boiler. However, because of the design and construction of fire-tube boilers, there is a definite limitation to their size and the pressure that they can tolerate. 

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