GB1600352A

GB1600352A - Power plant

Info

Publication number: GB1600352A
Application number: GB19172/78A
Authority: GB
Original assignee: Stal Laval Turbin AB
Current assignee: ABB Stal AB
Priority date: 1977-05-13
Filing date: 1978-05-12
Publication date: 1981-10-14
Also published as: IT7868098A0; SE7705654L; ES469748A2; JPS53140442A; DE2819379A1; FR2390580A1; SE405621B

Description

(54) POWER PLANT (71) We, STAL-LAVAL TURBIN AB, a Swedish Company, of Finspong, Sweden, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: This invention relates to a power plant of the kind comprising a steam boiler and a high pressure turbine and therebetween a separately fired superheater with a fluidised bed.

A power plant of the kind referred to has a control valve for the turbine, and the normal location of this valve is in the immediate vicinity of the turbine. This however, means that the pressure in the superheater is maintained when the control valve is closed or throttled. In a fluidised bed superheater this means that the tubes, because of the thermal inertia of the bed compound, are exposed simultaneously to a high pressure and a high temperature, which places great demands on the material of the tubes.

According to the present invention, in a power plant of the kind referred to a control valve for the turbine is arranged between the steam boiler and the superheater. In this way, the throttling of the superheater and thus the increased temperature in its tubes result in the pressure therein being reduced so that the tubes are never exposed to high pressure and high temperature simultaneously.

Another advantage of a power plant according to the invention is that the throttling of the control valve results in reduced steam pressure while, because of the expansion of the steam, the volume of the steam and thus also its velocity in the tubes in the superheater remain substantially unchanged. In this way the pressure fall across the tubes is maintained, which ensures a good distribution of the flow over all tubes and therefore an even heat transmission in the entire superheater.

The invention will now be described, by way of example, with reference to the accompanying drawing, the single Figure of which is a schematic diagram of the power plant described in our British Patent Specification No. 1550688 (Application No. 37358/ 76), but modified in accordance with the present invention.

The drawing shows a power plant comprising a steam boiler, generally designated by the numeral 1, which delivers steam to a high pressure turbine 2 and an intermediate pressure turbine 3. From the intermediate pressure turbine 3 the steam passes to a low pressure turbine (not shown) with an associated condenser. The condensate is passed through certain apparatus and low-pressure preheaters (not shown) and is returned to the boiler through high-pressure preheaters 4 and 5, heated by means of discharge steam from the intermediate pressure turbine 3 and the high-pressure turbine 2.

In addition to a boiler part 14, the steam boiler 1 may comprise an economiser 10, a steam dome 11 and a superheater 12. The steam dome may possibly house a heatexchanger for cooling steam which, from an output after the superheater 12, is conducted to an output 13. Alternatively, recooled steam may be produced by cooling steam from an output after the superheater 12 by spraying in feed water.

The plant further comprises a separately heated superheater 6, the tubes of which are immersed in a fluidised bed for cooling the same. Because of the particular combustion, physical and mechanical properties of the fluidised bed, it is possible to superheat up to 700"C or more without any of the disadvantages, for example in the form of high-temperature corrosion, which occur in boilers with common combustion devices and heating chambers. The combustion in the fluidised bed is controlled so that a substantially constant degree of superheat is obtained.

If, as shown in the drawing, an intermediate superheater 7 is provided between the two turbines 2 and 3, it should also be constructed as a fluidised bed superheater.

The power plant so far described is exactly in accordance with the power plant illustrated and described in the aforesaid specification.

In accordance with the present invention the plant has the control valve 15 of the turbine 2 located between the outlet side of steam boiler 1 and the inlet of the superheater 6. In this way regulation of the steam pressure is carried out before the superheater 6, and a permanent full steam velocity through the superheater 6 is achieved all the way down to the lowest load on the turbine 2.

If the control valve 15 had been positioned between the superheater 6 and the turbine 2, a reduction of the pressure of the turbine 2 would result in reduced steam velocity and thus increased temperature of the tubes at full pressure on these, while at the same time the flow distribution and thus the temperature distribution over the tubes would be deteriorated.

WHAT WE CLAIM IS: 1. A power plant comprising a steam boiler and a high pressure turbine and therebetween a separately fired superheater with a fluidised bed. characterised in that a control valve for the turbine is arranged between the boiler and the superheater.

2. A power plant constructed and arranged substantially as herein described with reference to, and as illustrated in, the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the fluidised bed is controlled so that a substantially constant degree of superheat is obtained. If, as shown in the drawing, an intermediate superheater 7 is provided between the two turbines 2 and 3, it should also be constructed as a fluidised bed superheater. The power plant so far described is exactly in accordance with the power plant illustrated and described in the aforesaid specification. In accordance with the present invention the plant has the control valve 15 of the turbine 2 located between the outlet side of steam boiler 1 and the inlet of the superheater 6. In this way regulation of the steam pressure is carried out before the superheater 6, and a permanent full steam velocity through the superheater 6 is achieved all the way down to the lowest load on the turbine 2. If the control valve 15 had been positioned between the superheater 6 and the turbine 2, a reduction of the pressure of the turbine 2 would result in reduced steam velocity and thus increased temperature of the tubes at full pressure on these, while at the same time the flow distribution and thus the temperature distribution over the tubes would be deteriorated. WHAT WE CLAIM IS:

1. A power plant comprising a steam boiler and a high pressure turbine and therebetween a separately fired superheater with a fluidised bed. characterised in that a control valve for the turbine is arranged between the boiler and the superheater.