Boiler Auxiliaries

Smooth starts are possible with steam turbine installations that include an auxiliary boiler because the startup phases of the turbocompressor can be matched to different plant operating conditions. Aside from process-related timing issues, the time elapse or machinery startup duration is generally determined by the temperature gradients admissible on both steam turbine and expander. These factors are influenced by the relative expansion rates of the fixed and rotating components in these machines. 

When restarting an installation that is still moderately hot, diffieulty is often experieneed during the initial phase due to the use of saturated steam (from the auxiliary boiler), whieh is eooler than the superheated steam raised by ammonia eombustion. Consequently, a sturdy steam turbine must be ehosen, eapable of withstanding the thermal stresses imposed. 

Where propulsion is provided by diesel or gas turbine, it is common to use an auxiliary boiler in conjunction with a waste heat/heat recovery boiler (WH/HR boiler). The steam-HW mixture, produced by passing the exhaust engine gases over the HR boiler tubes, is piped to the auxiliary boiler steam drum and then mixes with auxiliary BW. All steam utilized by the ship is taken from the auxiliary boiler. 

Fossil fuel-fired auxiliary boiler(s) from adjacent areas... 

This study case is designed as a free-standing hydrogen plant. Economies of operation could undoubtedly be obtained if this plant can be integrated with the utility system of an existing complex e.g. the 150,000 lb/hr of steam produced from the auxiliary boiler could be more efficiently included in the capacity of a larger boiler. 

Figure 46. Example of the heat recovery in leh convection section (top-fired furnace, plant with auxiliary boiler)...

The synthesis loop boiler on the exit of the converter is also a very important piece of equipment. In some modern plants not equipped with an auxiliary boiler it supplies nearly half of the total steam generation. It may generate as much as 1.5 t of steam per tonne of ammonia, equivalent to about 90% of the reaction heat. Fire-tube versions have been also used, including Babcock-Borsig s thin-tubesheet design. But compared to the secondary reformer service, where the gas pressure is lower than the steam pressure, the conditions and stress patterns are different. In the synthesis loop boiler the opposite is the case, with the result that the tubes are subjected to longitudinal compression instead of being under tension. Several failures in this application have been reported [993], and there was some discussion of whether this type of boiler is the best solution for the synthesis loop waste-heat duty. 

The earlier plants operated at deficit, and needed an auxiliary boiler, which was integrated in the flue gas duct. Auxiliary burners in tunnels or flue gas duet were additionally used in some instances. This situation was partially caused by inadequate waste heat recovery and low efficiency in some energy consumers. Typically, the furnace flue gas was discharged in the stack at rather high temperature because there was no air preheating and too much of the reaction heat in the synthesis loop was rejected to the cooling media (water or air). In addition, efficiency of the mechanical drivers was low and the heat demand for regenerating the solvent from the C02 removal unit (at... 

Partial oxidation ammonia plants have the same emission sources except for the primary reformer flue gas. The plants have an auxiliary boiler to generate steam for power production and fired heaters, which on account of the sulfur content of the fuel oil release a flue gas containing S02 (< 1500 mg/m3). Other possible emissions are H2S (< 0.3 ppmv), CO (30 ppmv) and traces of dust. The NO, content of the flue gas depends on the configuration of the auxiliary boiler and on the extent electric power generation on the site as opposed to outside supply. The total NO, emission per tonne of product may be somewhat lower than for steam reforming plants. 

Makeup Water Treatment Auxiliary Boiler Building... 

Auxiliary Boiler System Auxiliary Boiler (Electric) Condensate Makeup Pumps Feed Pumps and Valves Deaerator... 

MAKEUP WATER TREATMENT AUXILIARY BOILER BUILDING... 

The off-gases from the hydrogen recovery units described above are normally used as fuel somewhere else in the plant (typically reformer or auxiliary boiler). 

The reformer units, auxiliary boilers, and. sulfur recovery units should be monitored for NO and SOx concentrations. The monitoring frequency depends on local regulations. 

DOS Standby Diesel and Auxiliary Boiler Fuel System... 

The auxiliary steam boiler is an electric package boiler. It supplies the steam required during a cold start of the main steam system and the turbine-generator additionally, it provides the steam for hot water heating. Main steam supplements the auxiliary steam header during start-up, and it supplies the auxiliary steam during normal operation at power. The auxiliary boiler provides the steam during a plant shutdown. 

Rayaprolu, K. 2009. Boilers for Power and Process. Boca Raton, FL CRC Press. Divided into three sections (Boiler Fundamentals, Boiler Part and Auxiliaries, Boilers and Firing), this work addresses boiler heat and fluid flow basics, addresses the basic components and attachments of a typical boiler system, and discusses various ways of firing boiler systems. 

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