Your Answer : (Not Answered)

Correct Answer : D

Boiler rating is usually defined in terms of steam output in kg/hr.

A boiler's capacity is stated as the mass of steam it generates per hour, often as equivalent evaporation from and at 100 °C, which makes boilers working at different conditions comparable.

Steam temperature, heat transfer rate and heating area all affect performance, but none of them is the standard rating.

Your Answer : (Not Answered)

Correct Answer : A

The boiler mounting is the blow off cock.

Mountings are fittings mounted on the boiler for its safe operation: safety valves, water level indicator, pressure gauge, steam stop valve, feed check valve, fusible plug and blow off cock. The blow off cock drains water and sludge from the bottom of the boiler.

The feed pump, economizer and superheater are accessories, which improve efficiency but are not needed for safety.

Your Answer : (Not Answered)

Correct Answer : C

It is called firm power.

Firm power is the power a hydroelectric plant can supply continuously at all times, even in the driest period when stream flow is at its minimum. Because it is always available, it is the part of the output a utility can commit to supply.

Secondary power is the surplus above firm power, available only when flows are higher, so it cannot be guaranteed. Base power describes the load a plant carries, not the guaranteed output under adverse flow. Some texts treat 'primary power' as another name for the same idea, but the standard term for this definition, and the one the key uses, is firm power.

Your Answer : (Not Answered)

Correct Answer : B

The correct statement is that in a reaction turbine the expansion takes place in guide vanes and moving vanes both.

In a reaction turbine the steam or water expands, and its pressure falls, both in the fixed guide blades and in the moving blades, so the moving blades receive a reaction force as well as an impulse. The Parsons turbine is the classic case, with half the drop in each, a degree of reaction of 0.5.

In an impulse turbine the whole expansion happens in the nozzles or guide vanes and none in the moving blades, so option (A) is wrong. Its degree of reaction is therefore zero, not one, and a reaction turbine's is above zero, so (C) and (D) are both wrong.

Your Answer : (Not Answered)

Correct Answer : B

The excess air is closest to 7.4 %.

Take 100 g of fuel. In moles: C 6.5, H₂ 8, S 0.1, fuel O₂ 0.05. Stoichiometric oxygen:

\[ \begin{aligned} O_{2,st} &= 6.5 + \tfrac{8}{2} + 0.1 - 0.05 \\ &= 10.55\ \text{mol} \end{aligned} \]

With a fraction x of excess air, the dry flue gas holds CO₂ 6.5, SO₂ 0.1, excess O₂ 10.55x and N₂ 3.76 × 10.55(1 + x). SO₂ is 0.2% of it, so the dry gas totals 0.1/0.002 = 50 mol:

\[ \begin{aligned} 6.6 + 39.67 + 50.22x &= 50 \\ x &= 0.074 \end{aligned} \]

So about 7.4% excess air; the percentage is the same by mass, since the excess is a fraction of the same air. Water vapour is excluded because the analysis is on a dry basis; including it, or omitting the fuel oxygen, moves the answer away from the listed 7.4.

Your Answer : (Not Answered)

Correct Answer : A

The major problem is contamination of water.

Coal-bed methane is held in coal seams by water pressure, so to release the gas large volumes of groundwater must be pumped out. This 'produced water' is often saline and may contain sodium bicarbonate, metals and other contaminants; its disposal can pollute surface water and soil, and pumping lowers local water tables.

Carbon dioxide, nitrogen oxides and sulphur oxides arise when fuels are burnt, which is common to all fossil fuels and not specific to the production of coal-bed methane.

Your Answer : (Not Answered)

Correct Answer : A

The speed should be 375.0 rpm.

For the same turbine at the same efficiency, the velocity triangles must stay similar. Flow velocities scale as \(\sqrt{H}\), and so must the blade speed, so with the diameter fixed:

\[ \begin{aligned} \frac{N}{\sqrt{H}} &= \text{constant} \\ N_{2} &= 750\sqrt{\frac{5}{20}} = 750 \times 0.5 = 375\ \text{rpm} \end{aligned} \]

187.5 rpm scales the speed with H instead of its square root, and 750 rpm ignores the change of head. 524.5 rpm corresponds to neither relation.

Your Answer : (Not Answered)

Correct Answer : C

Energy is recovered by flashing the blowdown to generate low-pressure steam.

Blowdown is hot water drawn from the boiler at boiler pressure to limit dissolved solids. In a flash tank its pressure is reduced, part of it flashes to clean low-pressure steam that can feed the deaerator or process heating, and the remaining hot water can preheat the make-up water in a heat exchanger.

Blowdown cannot be avoided, because solids would build up and cause scaling and carryover. Recycling it to the drum or mixing it with feedwater would return the concentrated solids to the boiler, defeating its purpose.

Your Answer : (Not Answered)

Correct Answer : B

Friction in a steam nozzle reduces the mass flow rate. Friction reheats the steam, increases the dryness and lowers the enthalpy drop that becomes kinetic energy, so the exit velocity is lower and the specific volume at the exit is larger, which reduces the mass flow through the throat. The specific volume increases and the dryness fraction increases, and the actual enthalpy drop decreases, so the other three options state the reverse.

Your Answer : (Not Answered)

Correct Answer : C

In a reaction steam turbine the pressure drops in both the nozzle (fixed blades) and the moving blade channel. The steam expands partly in the fixed blades and partly in the moving blades, which is why the moving blades work by reaction as well as impulse. In an impulse turbine the pressure drops only in the nozzles, so the options of drop in the nozzle only, or in neither, are wrong.

In the Parsons turbine the stage has 50 percent reaction, where the pressure drop is shared equally between the fixed and the moving blades.

Your Answer : (Not Answered)

Correct Answer : C

The merit of a tidal power plant is that its power generation is not affected by rain, since tides come from the gravitational pull of the Moon and the Sun and not from rainfall. The initial cost of a tidal plant is high, construction at sea is difficult, and the power output does fluctuate with the tide, so the other statements are not merits.

Your Answer : (Not Answered)

Correct Answer : A

The advantage of a wind power plant given by the key is that there is no need for transportation facilities, because the wind is available everywhere and no fuel has to be carried to the plant. The availability of wind energy is not constant, wind conversion systems make noise from the blades and gearbox, and the structure is not described as simple in the key, so the other statements are wrong.

A wind plant needs no fuel, so there is no fuel to carry to it; its drawbacks are that wind is intermittent, the plant needs a large site and the blades and gearbox make noise.

Your Answer : (Not Answered)

Correct Answer : D

A load of railways, trolley buses and the like, with wide variations during peak and off-peak hours, is a traction load. Domestic load is that of lights and fans in homes, commercial load that of shops and offices, and industrial load that of factories, none of which is described by the variations of railways and trolley buses.

Your Answer : (Not Answered)

Correct Answer : A

The additional component of a closed cycle gas turbine over an open cycle is the heater. In the closed cycle the working gas is heated in a heater from outside, in place of burning fuel in the working fluid, and it is cooled in a cooler after expansion. The air compressor, the combustion chamber and the gas turbine are found in both cycles, but the combustion chamber is replaced by the heater in the closed cycle, so the heater is the item added.

Your Answer : (Not Answered)

Correct Answer : D

An open cycle gas turbine does not require a cooling medium. In the open cycle fresh air is drawn in each cycle and the hot exhaust gases leave to the atmosphere, so the heat is rejected with the exhaust. A closed cycle needs a cooler to return the working fluid to the initial state, and so it needs cooling. The options of cooling being required occasionally, in a small amount or in a large amount all go against this.

As the open cycle needs no cooler or condenser, it is the type used for aircraft engines and most gas turbine plants, where the exhaust carries the heat away.

Your Answer : (Not Answered)

Correct Answer : D

A dead weight safety valve is mainly used for low pressures, low capacity, stationary boilers of the Cornish type. In it a weight placed on the valve holds it on its seat, and the weight is lifted when the steam pressure rises, which makes it suited to low pressure. A spring loaded valve is used for higher pressure and for locomotives, a lever safety valve is used for stationary boilers with a heavier weight on a lever, and the high steam and low water valve gives a warning for both conditions, so the dead weight valve is the key.

Your Answer : (Not Answered)

Correct Answer : C

The Yarrow boiler is an example of a water tube boiler. In a water tube boiler the water flows inside the tubes and the hot gases pass over them. The Lancashire boiler is a fire tube boiler of the Cornish type with two flues, the Cochran boiler is a vertical multitubular fire tube boiler and the locomotive boiler is also a fire tube type, so those are not water tube boilers.

Other familiar water tube boilers are the Babcock and Wilcox, Stirling and La Mont boilers.

Your Answer : (Not Answered)

Correct Answer : B

The statement that is correct for water tube boilers when compared with fire tube boilers is that the various parts are more accessible. In a water tube boiler the water is in tubes and the hot gases are outside, which makes the tubes easy to inspect, clean and replace. Water tube boilers are suited to large power plants, they occupy less floor area for a given power, and they require more skill to work efficiently, so the other statements are wrong.

Your Answer : (Not Answered)

Correct Answer : C

The advantage of an injector for a boiler is that it has no moving parts, hence there are no dynamic parts. An injector uses a steam jet to raise the pressure of the feed water, so nothing in it rotates or reciprocates, which makes it simple. Its pumping efficiency is low, it cannot force very hot water into the boiler, and it does not work smoothly in extreme variation of load and pressure, so the other options are wrong.

The steam used by the injector condenses in the feed water, so its heat returns to the boiler, which is why the injector is a compact and cheap feed device on locomotives and small boilers.

Your Answer : (Not Answered)

Correct Answer : A

The feed check valve is a boiler mounting. Mountings are the fittings fixed on the boiler for its safety and control, such as the safety valve, stop valve, water level gauge, blow-off cock and the feed check valve. An injector, feed pumps and a steam trap are accessories or devices that work with the boiler and are not mountings in this classification.