Part-Load Operation

Part-load operating may reduce the ability of the trap to properly drain the condensate. This is especially true when low steam pressure is used and, when throttled at low loads, the pressure may fall below atmosphere or the pressure of the discharge header. Problems associated with this are discussed in Chapter 31. 

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Assessments of control, operabiHty and part load performance of MHD—steam plants are discussed elsewhere (rl44 and rl45). Analyses have shown that relatively high plant efficiency can be maintained at part load, by reduction of fuel input, mass flow, and MHD combustor pressure. In order to achieve efficient part load operation the steam temperature to the turbine must be maintained. This is accompHshed by the use of flue gas recirculation in the heat recovery furnace at load conditions less than about 75% of fiiU load. 

When used to eompress air, the axial eompressor may be equipped with adjustable stator blades, either partially (Figure 4-16) or on all stages. In the ease of a motor serving as the assoeiated driver or with a generator eoupled to the train, the adjustable stator blade feature allows more effieient eontrol than suetion throttling. With a steam turbine as the assoeiated driver, stator blade adjustment may be eombined with the obvious shaft speed eontrol. This eombination allows for speeial operating eonditions, sueh as startup, or extreme part-load operation. 

In unloaded or part-load operation, rod reversals must be of sufficient magnitude to provide lubrication to the crosshead bearings. The bearings are lubricated by the pumping action of the opening and closing of the bearing clearance area. 

For plant such as boilers, operating in parallel controls should ensure that one boiler acts as a lead to minimize part-load operation. As far, as is possible, plant should be sized to meet the load and oversizing should be avoided. 

Constraints can limit the degree of part load operation of a fuel cell. For example, a PAFC is limited to operation below approximately 0.85 volts because of entering into a corrosion region. 

The low cetane number of coal liquid fuels could lead to poor starting and warm-up characteristics at low ambient temperatures and to engine roughness at part load operation. 

In situations in which the data are not a representative sample, careful consideration needs to be given to the possibility of biases. A sample would be non-representative, for example, if it were obtained for conditions or situations different from those that are assumed in the analysis. For example, suppose that emissions were measured during steady-state full-load operation, but that one desired to make predictions of emissions during transient part-load operation. The available sample of data is not representative of the desired scenario. If inferences are made based upon such data without any correction or adjustment, it is possible that the mean emission rate will be biased and that the range of variation in emissions will be incorrectly estimated. 

Multiple-step variable-speed fan control, type d. is best applied with steam-turbine drives. In aplant with ac auxiliary motor drives, slip-ring motors with damper integration must be used between steps, making the installation expensive. Although dc motor drives would be less costly, few power plants other than marine propulsion plants have direct current available. And since marine units normally operate at full load 90 percent or more of the time, part-load operating economics are unimportant. If steam-turbine drive will be used for the fans, plot the power-input curve LMD, using data from the fan manufacturer. 

When compared to diesel fuel the emissions of CO and HC are higher for bio-oil. The results indicate slightly lower NOx emissions for bio-oil. All measurements were taken at part load operation due to the limitation of the gas turbine. The initial tests in dual-fuel-mode were performed with a relatively cold combustion at part load which may be the reason for the incomplete combustion of the hydro carbons. Also the combustion air fuel ratio was not adjusted for bio-oil operation at part load. The combustion of bio-oil is clearly recognised by the exhaust gas odour and a light exhaust gas cloudiness. 

While different developers are addressing improvements in individual components and subsystems in automotive fuel cell propulsion systems (e.g., cells, stacks, fuel processors, balance-of-plant components), we are using modeling and analysis to address issues of thermal and water management, design-point and part-load operation, and component-, system-, and vehicle-level eificiencies and fuel economies. Such analyses are essential for effective system integration. 

Compared to alkaline electrolysis, material costs are high for SPE electrolysers. The advantage of the SPE technology lies in a higher gas quality - especially in part load operation. Using a solid electrolyte also makes higher pressure possible as the absence of alkaline solution provides better sealing options. Some suppliers of SPE electrolysers are listed in Table 5.2. 

Fig. 8.31 En gine efficiency at 2000 rpm and part load operation of a hydrogen engine, compared to a current technology gasoline and diesel engine [54, 55],...

A further important difference is the achievable efficiency. For hydrogen operated PEFC efficiencies of about 60 % have been demonstrated in part load operation. For DMFC the various losses limit the maximum efficiency to about 25 %. 

The GT-off design performance has also been investigated by Naqvi et al [76], The use of C02-rich stream gas turbine is also included in the analysis, which accounts for 14% of the electric gross power produced. The net electric efficiency is around 52% in the case of maximum solid temperature of 1200°C (Figure 5.26), and the electric efficiency decay due to the part-load operation is lower than that in the conventional combined cycle (higher than 94% of the nominal electrical efficiency in the case of 54% of full load) if an advanced control strategy is adopted. 

IFLOW AMO STATIC PRESSURE OtSTfOBUnON M OBD PLATE AT FULL AW PART LOAD OPERATIONS. 

Therefore, it can be summarized that the combustion model (2.1)-(2.3) together with the fuel spreading extension (5.1) represents a suitable approach for the numerical simulation of a PFBC combustor. In [2] the models are derived in detail and are used to study the part-load operation behaviour and the feed point geometry of a PFBC plant. Finally, the simulation facilitates statements on the scale-up from a pilot plant to a large scale PFBC reactor. 

Performance characteristics of part-load operations of a solid oxide fuel cell/gas turbine hybrid system using air-bypass valves. /. Power Sources, 175, 296-302. 

Electric machines yield a much higher efficiency spreading over a wider area (Figure 35.6). It can exceed 90%, with a less pronounced drop towards part-load operation compared with internal combustion engines. 

SOFC technology, on the other hand, offers interesting options to improve the effectiveness of CHP units. The reasons are many the prospects for high efficiency, low emissions, low noise, scalability, reliabihty, and, finally, potentially low cost. However, the main attractiveness in CHP is the high system efficiency even for small units and at part load operation [14]. Among the most interesting applications are stationary distributed power generation (incl. CHP), small residential combined heat and power units (micro CHP), various transport apphcations (auxiliary power units, APU), and medium-sized portable systems up to 5 kWei-... 

In contrast to the Lurgi FBDB, the BGL product gas features more NH3 and more phenols and HCN. The moisture content of the raw gas is around 15vol% and mainly determined by the fuel moisture. The oxygen content of the raw gas is 3-10 ppmv. The minimum acceptable part load operation of the BGL gasifier... 

The operational options and characteristics associated with the plant to provide for part-load operation... 

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