Figure 5.1 Types of Superheaters: convective and radiant.

The convection superheater is placed somewhere in the gas stream, where it receives most of its heat by convection.

As the name implies, a radiant superheater is placed in or near the furnace, where it receives the majority of its heat by radiation.

The conventional convection-type superheater uses two headers into which seamess tubes are rolled or welded. The headers are baffled so that the steam is made to pass back and forth through the connecting tubes, which carry their proportioned amount of steam, the steam

Superheaters have many advantages:

i) Steam consumption of the engine or turbine is reduced.

ii) Losses due to condensation in the cylinders and the steam pipes are reduced.

iii) iii)Erosion of turbine blade is eliminated.

iv) Efficiency of steam plant is increased.

Words to be Known

superheated steam перегретый nap

heat loss потеря тепла

decreased steam rates уменьшен­ный расход пара

saturated steam насыщенный пар

superheating surface поверхность перегрева

reheater superheater промежу­точный пароперегреватель

to employ использовать

desuperheater пароохладитель

desuperheated steam охлажден­ный nap

to maintain поддерживать

uniform steam flow равномерный поток пара

radiant superheater радиацион­ный пароперегреватель

convection конвективный

gas passages газоходы

to exceed превышать

tensile strength предел прочности

shell корпус, кожух

safety valve предохранительный клапан

to discharge стравливать

I. Complete the statements. Choose the proper noun from the list.

caps, headers, rates, loss, the flue gases ,convection, furnace, reheat, saturation, surface

1. The radiant superheater is placed in the ... . 2. The heat is transmitted by ... . 3. The seamless tubes are rolled into the ... .4. Access to the tubes is had by .... 5. Superheating ... is exposed to steam and hot gases. 6. Superheated steam is transmitted over great distances with very little heat ... . 7. This steam is heated above the temperature of ... corresponding to the pressure. 8. Superheated steam results in decreased steam ... . 9. In some installations ... is used.10. An air preheater recovers some portion of the waste heat of the flue gases and utilizes it for preheating of air supplied to the combustion chamber of the boiler.

II. Answer these questions on the text

1. What are the advantages of superheated steam? 2. Has superheated steam reduced turbine-blade erosion to a minimum? 3. Can you say what steam is said to be superheated? 4. What is superheated surface? Explain. 5. What steam is required for the auxiliaries, superheated or saturated? 6. A desuperheater is usually placed in the steam drum, isn’t it? 7. What is the function of a desuperheater? 8. Say what general types of superheaters you know. 9. Where are radiant type superheaters placed? 10. Where are convection type superheaters placed? Are they often used on ships? 11. What does the convection type superheater consist of?

III. Translate into English

1. Пароперегреватель изготавливается из стальных труб, образующих поверхность нагрева для проходящего по ним пара.

2. Хотя пароперегреватель может быть выполнен в виде подключенного к котлу отдельного агрегата с собственной топкой, как правило, пароперегреватели встраивают в систему парогенератора.

3. Встроенные пароперегреватели бывают двух видов: радиационные и конвективные.

4. В зависимости от направления движения газов и пара различают три основные схемы вклю­чения пароперегревателя в газовый поток: прямоточную (а) — газы и пар движутся в одном направлении; противоточную (б) — газы и пар движутся в противоположных направлениях; смешанную (в) — в одной части пароперегревателя газы и пар движутся прямоточно, а в другой — в противоположных направлениях.

Economisers

Economisers are heat exchangers which are fitted in a boiler to increase the efficiency of the boiler. This is done by extracting the heat from the exiting gas and using it to heat the feed water entering the boiler.

The flue gases, having passed through the main boiler and the superheater, will still be hot. The energy in these flue gases can be used to improve the thermal efficiency of the boiler. To achieve this the flue gases are passed through an economiser.

The economiser is a heat exchanger through which the feedwater is pumped. The feedwater thus arrives in the boiler at a higher temperature than would be the case if no economiser was fitted. Less energy is then required to raise the steam. Alternatively, if the same quantity of energy is supplied, then more steam is raised. This results in a higher efficiency. In broad terms a 10°C increase in feedwater temperature will give an efficiency improvement of 2%.

The economiser is interposed between the boiler and the stack. The water is pumped through the econ­omizer on its way to the boiler. The gases leaving the boiler pass through the economizer before going to the stack. The heat absorbed by the water in passing through the econo­mizer would otherwise be lost. Economizers reduce the losses to a minimum.

An economizer consists of a series of tubes through which feed water flows, surrounded on the outside by the hot gases.

Present practice is to make the economizer an all-steel unit. The tubes are rolled into the headers. When headers are not employed, return bends are used. The ratio of boiler to economizer heating surface is about 2 to 1.

Economizers are parallel or counterflow-parallel when the gases and water flow in the same direction; counterflow when they flow in opposite directions. The counterflow is considered to be the more effective, resulting in a greater heat transfer. In the counterflow, the gases leaving the boiler enter the economizer at the end from which the water makes its exit.

Words to be Known

feed-water heater подогреватель питательной воды

flue gases топочные газы

to interpose размещать

stack дымовая труба

to lose (lost; lost) терять

series of tubes ряд трубок

all-steel unit стальной узел

return bend обратное колено трубы

flange joints фланцевые соединения

to range колебаться в пределах

ratio соотношение

counterflow противоток

opposite противоположный

heat transfer теплопередача