RU2091666C1 - Method of cooling steam drum boiler - Google Patents

Abstract

FIELD: boiler engineering; boilers equipped with devices of steam cooling of drum in transient modes. SUBSTANCE: cooling the steam drum boiler is effected by feeding the steam to drum cooling device from external source, discharging steam continuously in course of cooling and ventilating after shut-down of boiler. Then drainage of water is started at excessive pressure. Drainage is effected through drain holes provided in lower points on boiler and after drainage of water, supply of steam from external source is discontinued. EFFECT: depression of inoperative corrosion and reduction of time required for cooling. 3 dwg

Description

 The invention relates to the field of boiler technology, in particular to the operation of boilers equipped with devices for steam cooling of the drum in transient conditions.

Known methods for cooling drum boilers do not provide for draining water from the boiler at overpressure, and the current "Rules for the technical operation of power plants and networks" allow the draining of water from a stopped boiler only after the pressure in it drops to atmospheric [1]
The reason for this limitation is the insufficient reliability of the cooling unit, the "connecting fitting-wall of the drum", in which, when using milling joints, leaks occurred due to increased thermal stresses.

A known method of cooling a steam drum boiler, selected as a prototype, which consists in supplying saturated steam to a steam cooling device from an external source, continuous in the process of damping the boiler, discharging steam supplied to the drum cooling devices through the end sections of the steam lines, ventilation of the furnace and flues immediately after stopping boiler [2]
The disadvantages of this technical solution are:
high corrosion rate of the inner surface of the drum and the pipe system due to the presence of water and, as a consequence, the development of cracking in the drums, collectors and bends of unheated pipes [3]
sufficiently long cooling of the boiler, especially at the final stage (below 100-180 ^o C), associated with a very slow cooling of a significant amount of boiler water (from 100 to 200 tons).

 The technical problem to which the invention is directed is the suppression of parking corrosion, reducing the duration of cooling.

 To solve the problem by a known method, cooling a steam drum boiler, which consists in supplying steam to the device for steam cooling of the drum from an external source, ventilation after stopping the boiler and continuous release of steam during the cooling process, at excess pressure, water is drained through the drainage of the lower points of the boiler, and the supply of steam from an extraneous source is stopped after draining the water.

 In FIG. 1 shows a drum with a steam cooling device in cross section; in FIG. 2 is a longitudinal section through the vertical plane of the drum; in FIG. Figure 3 shows the cooling graphs of the unit "connecting fitting wall of the drum" with various methods of stopping the boiler. The arrows show the direction of steam flows from the holes of the guide pipes.

A device for implementing the proposed method comprises a drum, a bubbler device 2 located therein, a throttle ceiling 3, a cyclone with a pallet 4, a drum steam cooling device containing an upper manifold 5, a lower 6 with guide tubes (not shown), steam supply lines from an external source 7 and 8. Carry out the method as follows. When the boiler stops (the mode with the water level in the drum), the temperature difference between the upper and lower components of the drum reaches from 80 to 120 ^o C. lower 6 distribution manifolds. Then, through the openings of the guide tubes, steam is supplied to the wall region of the drum and intensifies the heat transfer between the wall of the drum and the steam. This is explained by the turbulization of steam flows, the elimination of stagnant zones, and an increase in the speed of the steam washing the wall.

 Continuously in the process of cooling the boiler, the exhaust steam is discharged through the end sections of the steam pipelines.

 Ventilation of the furnace and flues begins immediately after the boiler stops. The ventilation mode is selected depending on the design features and operating conditions of the equipment.

The descent of water from the boiler begins at overpressure through the drainage of the lower points of the boiler (not shown). The pressure level is selected depending on the design of the boiler and the characteristics of the thermal scheme of the TPP and can be from 3 to 15 kgf / cm ² . The steam supply from an external source is stopped after the water is drained, which allows all the water to be displaced by the steam through the lower points of the boiler. The tests of the cooling mode of the boiler with the drain of water at overpressure were carried out by Uraltehenergo JSC on the boilers TGM-84B and TGME-464 of KamAZ TPP.

In FIG. Figure 3 shows the cooling pattern of the unit "connecting unit - drum wall" with different stopping methods with the following notation:
Operations: I boiler stopped;
II turned off the power to the boiler;
III connected RROU;
IV opened the drainage of the lower points of the screens, economizer, etc.

 V. Launch TDM for cooling.

Designations: 1 8 numbers of thermocouples;
9 wall of the drum;
10 fitting;
a stop without steam cooling and without maintaining the water level in the drum;
b stop with steam cooling without maintaining the water level in the drum;
to a stop with steam cooling of the drum and maintaining the "average" water level.

The graphs show that the temperature difference in the specified node with the proposed method (b) of cooling is insignificant and ranges from 8 to 10 ^o C. For comparison, the mode with the water level in the drum (c) is shown, when cooling is carried out in the most favorable conditions by maintaining the boiler level water on the saturation line. Moreover, the indicated temperature difference does not exceed 4-8 ^o C. This means that the descent of water from the boiler while maintaining the average level in the drum is impossible. Without the use of a drum cooling device, this difference can reach up to 40 ^o C, and in some cases significantly higher.

Tests have shown: the discharge of water from the boiler at overpressure provides drying of the inner surface of the drum, collectors and pipes due to the heat accumulated by the metal, lining and insulation, which significantly reduces the corrosion rate. So, if the water was drained at 36 kgf / cm ² , then the metal of the drum and pipe system remains at a temperature corresponding to saturation, 158 ^o C, and with a further decrease in pressure to atmospheric, the internal surfaces of all elements of the boiler are dried.

 The proposed method is much simpler and cheaper than the known chemical method of suppressing parking corrosion by introducing hydrazine into boiler water. In addition, the use of hydrazine is excluded in many emergency conditions, as well as during shutdowns in scheduled repairs for a long period with the discharge of water from the boiler.

 The discharge of water from the boiler significantly reduces the duration of its cooling (from 2 to 3 hours), because the heat contained in the water ranges from 50 to 70% of the total heat accumulated by the boiler.

 Currently, the issue of mass use of the regime on all drum boilers equipped with a steam drum cooling device is being addressed.

Claims (1)

 The method of cooling a steam drum boiler, which consists in supplying steam to the drum cooling device from an external source, continuously releasing steam during cooling and ventilation after stopping the boiler, characterized in that, at excessive pressure, water is drained through the drainage of the lower points of the boiler, and steam is supplied from an extraneous source is stopped after draining the water.

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