Vacuum pump for steam activated

Steam Vacuum Pump for Thermal Power Plant

Absrtact: This paper expounds the application of direct steam supply from power plant in molten steel vacuum treatment system by means of temperature and pressure reducing device, which solves the contradiction between enterprise development, energy saving and emission reduction targets and environmental protection.

Key words: vacuum treatment of temperature and pressure reducing steam

Vacuum pump for steam activated

1.Questions raised

In order to meet the needs of increasing production capacity, a new 80t EAF, two 150t LF/VD (VCD) on-line refining furnaces and six 200t-600t ingot vacuum pouring tanks have been built in Heavy Industries. Two new 400kg/h and 500kg/h steam jet vacuum pumps must be built to match them. With 250 kg/h and 300 kg/h steam ejection vacuum pumps for the original steelmaking equipment, the maximum flow rate of superheated steam is 40 t/h.

The company’s boiler room used to have two 10-ton coal-fired boilers. The steam produced is only enough for the original 250 kg/h and 300 kg/h steam injection pumps.

With the construction of 400 kg/h and 500 kg/h steam ejector pumps, the demand for steam is increasing, and the new steam equipment is restricted by the influence of energy saving and emission reduction targets and environmental protection policies.

2. Requirements of Steam Point for Vacuum Treatment of Molten Steel for Steam Quality and Flow Rate

1. Steam quality requirements for steam use points (four vacuum jet pumps with drums):
(1) Steam pressure: 0.87MPa + 0.02Mpa;
(2) Steam temperature: superheat at this pressure (20-30 C) + 2 C;
(3) Steam use time is random, four pumps are random combination start, the maximum number of pumps used at the same time is three;
(4) The use of adjacent two times of steam is discontinuous and the interval is 0.5-72 H.
(5) According to the starting sequence of the vacuum pump, the steam flow rate increases by leaps and bounds. At the end of the treatment, the maximum flow rate decreases sharply from about 12 t/h to 3-4 t/h or “0”;

2. Steam flow design:
(1) Steam flow rate for each vacuum pump is shown in Table 1.

Vacuum pump

Minimum flow (t/h)

Maximum flow (t/h)

250kg/h

 9

12

300kg/h

3

10.5

400kg/h

2.5

9

500kg/h

2.65

11

Table 1: Steam flow rate for each vacuum pump

(2) Flow design:
Maximum flow rate: according to the simultaneous operation of any three pumps, 35-40 t/h design;
Minimum flow rate: calculated by the minimum flow rate of 400 kg/h vacuum pump working alone, designed by 2.5 t/h;

Steam Supply Solutions
In order to ensure the progress of the project, the following five solutions are put forward after discussion and demonstration. See: (Table 2)

Steam Solution

Advantage

shortcoming

1

20t Coal-fired Boiler

Low Investment and Operation Cost

Limited by Energy Saving and Emission Reduction Indicators and Environmental Protection

2

80t Arc Furnace Waste Heat Boiler

Waste heat utilization

Limited Steam Production and Large Investment of Waste Heat Boiler

3

20t Gas Boiler

Low investment, strong adaptability and good mobility

Steam production costs are higher

4

Direct Steam Supply in Power Plant

The steam supply is reliable and the cost of steam is 15% lower than that of coal-fired boilers. The pipeline is long and needs to be solved such problems as temperature drop, hydrophobicity and water hammer.

5

Mixed Combustion Steam Generation System

Refining is simple, investment is saved and thermal efficiency is as high as 98%.

Steam costs are high, producing 6.9% water insoluble gas CO2 in the steam.

Table 2 Steam Supply Solutions

From the above analysis, it can be seen that scheme 4: direct steam supply of power plant is the best solution.

There are two 165 MW pumped cogeneration units in the local thermal power plant. The designed pumping capacity is 1.47 Mpa, 274 C and steam.
The steam flow rate is 335 *2=670 t/h, and the maximum single unit extraction capacity is up to 400 t/h. This steam is used for urban heating. In the off-season of urban heating, in order to ensure the normal power generation of two 165 MW units, a set of 75NW turbogenerator units is used as regulating steam load. Steam in power plant can fully meet the demand of 40 t/h in our company. Steam is piped to the temperature and pressure reduction station, then adjusted by the temperature and pressure reduction device to supply steam jet pump. The cost of direct steam supply in power plant is 15% lower than that of coal-fired boiler.

Direct Steam Supply Flow in Power Plant:

Steam is exported from the power plant to the entrance of the company. The length of the steam pipeline is 1200 meters (buried), and the diameter of the pipeline is D630 *9. From the entrance of the company to the vacuum temperature and pressure reduction device for molten steel treatment, the length of the steam pipeline is 1100 meters (overhead), and the diameter of the pipeline is D426 x9. After temperature and pressure reduction, steam is distributed from two branch pipes to 250 kg/h, 300 kg/h vacuum pump and 400 kg/h, 500 kg/h vacuum pump, each of which is about 150-200 m long. Thereby, according to the different flow rate, time interval of steam use and steam parameters at each point of use, the steam entering the pipeline should be treated with temperature, pressure or pressure reduction to ensure the steam requirement of the steam using point.

In the actual operation process, the device can quickly adapt to sudden changes in load. When the fault of decompression and temperature reduction is detected, it can respond quickly, switch in time, and ensure normal steam use when switching. The above design can give full play to its effectiveness, make the system achieve the desired control function, fully meet the strict requirements of continuous, accurate and stable operation.

Application effect:

It has been five years since the project was completed and put into operation in 2008. The steam pipe network and the temperature and pressure reducing device are reliable, and the steam supply is stable, which meets the demand of vacuum degassing of molten steel after expansion.
Since four vacuum jet pumps used direct steam from power plants, two 10 t coal-fired boilers have been shut down. The company has reduced energy saving and emission reduction targets. At the same time, the price of direct steam supply in power plant is 15 yuan lower than that of coal-fired boiler steam per ton. According to the current production of vacuum degassing molten steel in our company, millions of yuan can be saved annually, and the investment of temperature and pressure reduction device can be recovered in one year.

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