Fuel supply

FIGURE 16.4 Schematic image of a bipolar electrode view of anode (a) and cathode (b) sides. (Reproduced with permission from Ref [16]. Copyright 2010, The Electrochemical Society.) 

As described previously, despite the maximum power performance for a cathode fed directly with oxygen, the design is not practical because of its technical requirements, safety, cost, and its need for the user to service the feed system. It may be more feasible, however, to supply a low-pressure, low flow rate compressed air feed leveraged from other parts of the system, in a passive form. Oxidizer feed supply may be necessary for special applications in which not enough ambient oxygen or air is available. In general, for a low power generating EFC system, it is envisioned that passive di sion of ambient air to the cathode is the most technically viable approach. 

Because of much higher enzyme stability in the dried (lyophilized) state in comparison with hydrated enzymes, it is perceived that EFCs will be delivered dry and users will activate them by filling with fuel just before required operation. This has to be 

ENZYMATIC FUEL CELL DESIGN, OPERATION, AND APPLICATION 

---

When electricity is bought from centralized power generation companies, the price tends to be more stable than fuel costs, since power generation companies tend to negotiate long-term contracts for fuel supply. 

Evaluations of fuel resources or total fuel supply focus on critical economic and environmental issues as well as existence. These issues include avadabihty, utilisation patterns, environmental consequences, and related economic considerations. 

There are, however, a variety of other sources of methane that have been considered for fuel supply. Eor example, methane present in coal (qv) deposits and formed during mining operations can form explosive mixtures known as fire damp. In Western Europe, some methane has been recovered by suction from bore holes drilled in coal beds and the U.S. Bureau of Mines has tested the economic practicaUty of such a system. Removal of methane prior to mining the coal would reduce explosion ha2ards associated with coal removal. As much as 11.3 x 10 (400 trillion (10 ) cubic feet or 400 TCE) of... 

Most theories of droplet combustion assume a spherical, symmetrical droplet surrounded by a spherical flame, for which the radii of the droplet and the flame are denoted by and respectively. The flame is supported by the fuel diffusing from the droplet surface and the oxidant from the outside. The heat produced in the combustion zone ensures evaporation of the droplet and consequently the fuel supply. Other assumptions that further restrict the model include (/) the rate of chemical reaction is much higher than the rate of diffusion and hence the reaction is completed in a flame front of infinitesimal thickness (2) the droplet is made up of pure Hquid fuel (J) the composition of the ambient atmosphere far away from the droplet is constant and does not depend on the combustion process (4) combustion occurs under steady-state conditions (5) the surface temperature of the droplet is close or equal to the boiling point of the Hquid and (6) the effects of radiation, thermodiffusion, and radial pressure changes are negligible. 

Most of the commercial gas—air premixed burners are basically laminar-dow Bunsen burners and operate at atmospheric pressure. This means that the primary air is induced from the atmosphere by the fuel dow with which it mixes in the burner passage leading to the burner ports, where the mixture is ignited and the dame stabilized. The induced air dow is determined by the fuel dow through momentum exchange and by the position of a shutter or throtde at the air inlet. Hence, the air dow is a function of the fuel velocity as it issues from the orifice or nozzle, or of the fuel supply pressure at the orifice. With a fixed fuel dow rate, the equivalence ratio is adjusted by the shutter, and the resulting induced air dow also determines the total mixture dow rate. 

If the substitute fuel is of the same general type, eg, propane for methane, the problem reduces to control of the primary equivalence ratio. For nonaspiring burners, ie, those in which the air and fuel suppHes are essentially independent, it is further reduced to control of the fuel dow, since the air dow usually constitutes most of the mass dow and this is fixed. For a given fuel supply pressure and fixed dow resistance of the feed system, the volume dow rate of the fuel is inversely proportional to. ypJ. The same total heat input rate or enthalpy dow to the dame simply requires satisfactory reproduction of the product of the lower heating value of the fuel and its dow rate, so that WI = l- / remains the same. WI is the Wobbe Index of the fuel gas, and... 

This senses the speed of the machine and performs extremely fast and accurate adjustments in the fuel supply to the PM. In turn it regulates the speed and the output of the PM within predefined limits, depending upon the droop of the PM. The governor may be a mechanical (manual), hydraulic or electronic (automatic) device. 

This is to cut off the fuel supply to the engine on a trip or a normal stop of the engine. 

Active power (kW) sharing By changing the mechanical torque of the prime mover by changing its driving force (fuel supply). 

However, not all the hydrogen that is produeed is used in the produetion of methanol. To prevent an exeessive buildup of hydrogen in the reeireulating methanol synthesis loop, a slipstream is drawn off eonsisting of hydrogen and some CO and CO2. It is fed to the boiler as supplemental fuel to the main natural gas fuel supply. The slipstream is at approximately 800 psi pressure and must be redueed to 75 psi before it ean be fed to the boilers. 

What are current and potential fuel supplies In many areas natural gas is already in short supply. It may not be possible to convert a large plant with current allocations or pipeline capacity. 

Reference 3 speaks of controlling the excess air at 10% for plants having highly variable fuel supplies by using gas density to control air/ftiel ratio. Reference 3 gives the following equations relating theoretical air and density. 

CPD Compressor discharge of product D FUELM Fuel supply in addition to product A going... 

The liquid fuel handling components of the fuel system include the fuel filler pipe, fuel tank, fuel pirmp, and the fuel supply and return lines. The fuel tank is a low pressure, low hydrocarbon emission vessel designed to contain both the liquid and vapor phases of the fuel. An electric pump located inside the fuel tank is used to transfer liquid fuel from the tank to the engine. The fuel in the tank is suctioned from a small reservoir in the tank which minimizes liquid level transients caused by vehicle motion. 

Fuel - Fuel supplies to boilers, furnaces, gas turbine and engine drivers, etc., are designed with features such as multiple fuels, propane vaporizer backup, and a liquid fuel surge tank, to promote reliabihty. The failure of any one fuel to a process unit or utihty generation facihty is used as the basis for evaluating a potential overpressure. 

Two Workers Die and Solid Rocket Fuel Supply Destroyed ... 

The advantages of thermal incineration are that it is simple in concept, has a wide application, and results in almost complete destruction of pollutants with no liquid or solid residue. Thermal incineration provides an opportunity for heat recovery and has low maintenance requirements and low capital cost. Thermal incineration units for small or moderate exhaust streams are generally compact and light. Such units can be installed on a roof when the plant area is limited. = The main disadvantage is the auxiliary fuel cost, which is partly offset with an efficient heat-recovery system. The formation of nitric oxides during the combustion processes must be reduced by control of excess air temperature, fuel supply, and combustion air distribution at the burner inlet, The formation of thermal NO increases dramatically above 980 Table 13.10)... 

It is convenient for exergy tabulations to associate the term [ —AGq] = Grq — Gpo with the exergy of the fuel supplied (of mass My), i.e. ,0 = [—AGoJ. For a combustion process burning liquid or solid fuel (at temperature Tq) with air (subscript a, at temperature T"]), the left-hand side of the equation may be written as... 

A similar argument can be used for a fuelled semi-closed cycle, assuming that it can be regarded as the addition of an open CBT plant and a closed CHT cycle with identical working gas mass flow rates (and small fuel air ratios). Suppose the latter receives its heat supply from the combustion chamber of the former in which the open cycle combustion takes place. If the specific heats of air and products are little different, then the work output is doubled when the two plants are added together, but the fuel supply is also approximately doubled. The efficiency of the combined semi-closed plant is, therefore, approximately the same as that of the original open cycle plant. 

A second criterion of performance sometimes used is an artificial thermal efficiency (tja) in which the energy in the fuel supply to the CHP plant is supposed to be reduced by that which would be required to produce the heat load (Qu) in a separate heat only boiler of efficiency (tjb). i e- by (Qu/ b)- The artificial efficiency (tja) is then given by... 

In addition, they are usually constructed without isolation valves on the fuel supply lines. As a result the final connection in the pipework cannot be leak-tested. In practice, it is tested as far as possible at the manufacturer s works but often not leak-tested on-site. Reference 32 reviews the fuel leaks that have occurred, including a major explosion at a CCGT plant in England in 1996 due to the explosion of a leak of naphtha from a pipe joint. One man was seriously injured, and a 600-m chamber was lifted off its foundations. The reference also reviews the precautions that should be taken. They include. selecting a site where noise reduction is not required or can be achieved w ithout enclosure. If enclosure is essential, then a high ventilation rate is needed it is often designed to keep the turbine cool and is far too low to disperse gas leaks. Care must be taken to avoid stagnant pockets. 

Note that the operation of an emergency isolation valve should automatically shut down any pump in the line and trip the fuel supply to any furnace. 

A furnace was protected by a relief valve on its inlet line (Figure 10-1). A restriction developed after the furnace. The relief valve lifted and took most of the flow. The flow through the furnace tubes fell to such a low level that they overheated and burst. The low-flow trip, which should have isolated the fuel supply to the furnace when the flow fell to a low value, could not do so because the flow through it was normal. 

The furnace was fitted with interlocks that should have isolated the fuel supply if the tube wall temperature or the pressure of the heat transfer oil got too high. Neither interlock worked, and neither had been tested or maintained. The set-point of the high tube wall interlock had been raised far above its original set-point, from 433°C to 870°C, a simple way of putting it out of action [15]. Changing the set-point of an interlock is a modification and should be allowed only when the equipment is capable of withstanding the new conditions (see Chapter 2). 

---