Boilers temperatures

A PFBC boiler is visually similar to an AFBC boiler. The combustor is made of water-wall tubing, which contains the high-temperature environment, but the whole assembly is placed within a pressure vessel. Unlike an AFBC unit, there is no convection pass, as the flue-gas temperature must be maintained at boiler temperature to maximize energy recovery by the expansion turbine. There is an economizer after the turbine for final heat recoveiy. A simplified schematic is presented in Fig. 27-49. An 80-MWe demonstration plant, operating at 1.2 MPa (180 psia), began operation in 1989 with a power producdion intensity of 3 MWe/m (1 MWe/3.5 fU). By 1996, five units of this size had been construcded, and a 320-MWe unit is planned to commence operation in 1998. 

The heat transfer oil control valve was leaking. Unknown to the operators, the boiler temperature rose from 75°C to 143°C, the boiling point of the contents. Finally, bumping in the boiler caused about 0.2 ton of liquid to be discharged through the vent. 

Solid alkalis Solid alkalis may be used, in principle, for the corrosion control of drum boilers at all pressures but other factors, e.g. carryover or hideout a (reversible disappearance from solution on-load), may preclude them in some cases. However, they are used for feed-line treatment only in lower pressure plant where the boiler has increased tolerance to the higher solids burden which their use entails. Sodium hydroxide or, at very low pressures, sodium carbonate, (which is hydrolysed to the hydroxide at boiler temperatures) have been used, as have potassium and lithium hydroxides and various phosphate mixtures. (For a comparison of various alkalis for this purpose see References.)... 

Consequently, when selecting and blending the various raw materials used in all-polymer/all-organic formulations, the questions of thermal and hydrolytic stability and ability to transport or otherwise control colloidal iron oxides (in addition to possible adverse effects such as copper corrosion) become increasingly important at higher boiler temperatures and pressures. 

The various functional properties of neutralizing amines, such as basicity, neutralizing capacity, DR, and volatility often have little or no direct relationship with each other, but all these properties are significantly different at boiler temperatures. This vital consideration is often insufficiently highlighted in manufacturers data sheets. Consequently, some of the commonly available information comparing amines records data at ambient temperatures, making it next to useless. 

The degree of slagging, is, in turn, closely related to the concentration of vanadium, nickel, and sodium compounds present in the fuel, and the types of low melting-point oxides and complex sticky deposits formed under specific boiler temperatures and prevailing conditions. These deposits are difficult to remove online with soot blowers, but... 

COMMENTS (1) The sensitivity diagram of cycle efficiency versus boiler pressure demonstrates that increasing the boiler pressure increases the boiler temperature. This raises the average temperature at which heat is added to the steam and thus raises the cycle efficiency. Operating pressures of boilers have increased over the years up to 30 MPa (4500psia) today. 

The thermal efficiency of the Rankine cycle can be significantly increased by using higher boiler pressure, but this requires ever-increasing superheats. Since the maximum temperature in the superheater is limited by the temperature the boiler tubes can stand, superheater temperatures are usually restricted. Since the major fraction of the heat supplied to the Rankine cycle is supplied in the boiler, the boiler temperatures (and hence pressures) must be increased if cycle efficiency improvements are to be obtained. 

Determine the efficiency and power output of a regenerative Rankine (without superheater or reheater) cycle, using steam as the working fluid, in which the condenser temperature is 50° C. The boiler temperature is 350°C. The steam leaves the boiler as saturated vapor. The mass rate of steam flow is 1 kg/sec. After expansion in the high-pressure turbine to 100°C, some of the steam is extracted from the turbine exit for the purpose of heating the feed-water in an open feed-water heater the rest of the steam is then expanded in the low-pressure turbine to the condenser. The water leaves the open feed-water heater at 100°C as saturated liquid. 

The closed OTEC cycle as shown in Fig. 2.29 uses a secondary thermodynamic working fluid such as ammonia or freon to reduce the size of the plant. For a boiler temperature of 25°C, the vapor pressure... 

Condenser temperature Boiler temperature Mass flow rate of ammonia... 

In the bottom cycle, the freon condenser (CLRl) temperature is 20°C, and the freon boiler temperature is 35°C. There is no superheater in the freon cycle. 

A cogeneration cycle as shown in Fig. 5.19 is to be designed according to the following specifications boiler temperature = 500° C, boiler pressure = 7 MPa, condenser pressure = 5 kPa, process steam (cooler 2) pressure = 500 kPa, mass rate flow through the boiler = 15 kg/sec, and mass rate flow through the turbine = 14 kg/sec. 

The cogeneration cycle as shown in Fig. 5.19 is to produce power only according to the following specifications boiler temperature = 500°C,... 

For example, spheres of narrow size distribution of polyl/Mm-butylstyrene) were obtained by exposing the corresponding monomer droplets to the trifluorometh-anesulfonic acid initiator vapor (Fig. 1.5.8). The polymer particles ranged in diameter from I to 3 p,m, and their uniformity was sensitive to the monomer-to-initiator mass ratio. Under certain conditions the normally smooth spheres appeared connected through polymer whiskers (Fig. 1.5.9) (67). Using styrene monomer and adjusting the boiler temperature, uniform polystyrene particles up 10 xm in diameter and spheres of 20 p,m of broader size distribution could be prepared (67). 

Fig. 1.5.11 Scanning electron micrograph (SEM) of mixed metal hydrous oxide particles generated from mixed Ti(OEt)4 and A1(a -OBu)3 vapors at flow rate of 1.51 dm3 min-1 and boiler temperatures of 75°C and I25°C. (From Ref. 71.)...

Problem A steam engine operates with a boiler temperature of 200°C. What is the maximum theoretical efficiency of the engine if operated on a warm summer day (+30°C) compared with a cold winter day (— 30°C) How much more fuel will be required to perform the same work in the former case ... 

Solution With boiler temperature 7h = 200°C = 473K, the maximum (reversible) efficiency warm on a warm day with Tc = 30°C = 303K is determined from (4.22) to be... 

While the actual efficiency of any real steam engine falls below the theoretical optimum values calculated above, the improved fuel economy of operating the engine with higher boiler temperature Th or reduced exhaust temperature Tc is well known to steam engineers. 

In a 2-1. three-necked flask fitted with stirrer, dropping funnel, and thermometer are placed 700 ml. of formic acid (88%) and 140 ml. of hydrogen peroxide (30%, 1.37 moles). While the temperature is kept at 35-40° (Note 1), 116.2 g. (117.3 ml., 1.00 mole) of indene (98%) (Note 2) is added dropwise, with stirring, over a period of 2 hours. An additional 100 ml. of formic acid is used to rinse the last of the indene from the dropping funnel into the reaction flask. The reaction solution is stirred at room temperature for 7 hours to ensure complete reaction (Note 3). The solution is transferred to a 2- or 3-1. Claisen flask, and the formic acid is removed under aspirator pressure (b.p. 35-40°/20-30 mm), care being taken to maintain the boiler temperature below 60° (Note 4). The residue, after being cooled to room temperature, is a yellowish brown crystalline solid (Note 5), the color being due to contamination by a small amount of brownish oil. 

Boiler temperatures also influence the leachable amounts of elements in low fusion fly ashes. 

All boiler temperatures were measured just prior to and after the collection of the coal samples and their respective fly ashes, since it was physically impractical to collect the samples and measure the temperatures at the same times. In all cases, the temperatures remained essentially constant. An optical pyrometer was used to measure flame temperatures, and water-cooled jacketed thermocouples were used to monitor the boiler temperatures. The wall effects on the temperature measurements were minimized by insertion of the thermocouple into the boiler until temperatures remained constant with distance upon further insertion of the thermocouple into the boiler. 

The three different type of boilers used in this study were found to exhibit different temperature profiles. The flame and boiler temperatures monitored in Boiler A, when measured, were observed to be well below the initial deformation temperature of the ash (see Table II). On the other hand, the flame temperatures encountered in the B and D boilers were above the initial deformation point of the ash, and in some cases above the temperature at which the ash becomes fluid. In addition, the temperatures monitored in... 

The results of monitoring the temperature profiles and ash fusion temperatures of the ash resulting from the test coals burned in the different boilers indicated that the effect of boiler temperature and ash fusion characteristics of the coal on the leaching and sorbent characteristics should be examined. This could be carried out through a comparison of the leaching and sorbent characteristics of the fly ash produced in the 11 boiler with that produced in 12 boiler and the fly ash produced in the A boiler with that produced in the C and D Boilers, respectively. 

The boiler temperatures in the 11 boiler were observed to be 400-600 degrees higher than those measured in 12 boiler. The difference in temperature was especially pronounced in the arch region of the boilers. These temperatures indicate that the fly ash in the 11 boiler was exposed to higher temperatures for longer period of time in the fusion state than the fly ash in 12 boiler. 

Similar events also seem to have occurred with the boiler C and D fly ashes. Both fly ashes also generate alkaline leachates (see Table II). A comparison of the boiler temperatures that produced the boiler C and boiler D fly ashes and their ash fusion temperatures suggest that the boiler temperatures were high enough to cause fusion of their respective fly ashes within the boilers. Temperatures of 2600 and 2700°F were measured above the flame basket in the boiler C and boiler D, respectively. This is some 200° above the softening temperatures of the fly ashes. Apparently, the high temperatures encountered by the fly ash in the B boilers, boiler C and boiler D, have resulted in fusion reactions that have led to alkaline products that can be dissolved upon contact with water to form alkaline leachates. 

It can be seen from Table II that the fly ashes produced in the A boiler essentially form acidic leachates even though the major element composition of these fly ashes were comparable to the amounts found in the boiler C and boiler D fly ashes (see Table III). The Militant, Deep Hollow, Upshur and Badger fly ashes produced in this boiler encountered flame and boiler temperatures that are below even the initial deformation temperatures of the fly ash. Hence, the fusion reactions probably did not occur that might have led to formation of products that generate an alkaline leachate. 

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