Main technical indicators of nitrogen machine

Nitrogen production (Nm3/h) 400

Nitrogen purity (%) : 97

Outlet pressure (Mpa) : 1.1

Starting time (min) : 10

Installed capacity (KW) : 190

Overall dimensions: (3.0×1.1×1.4)×3

Number of flat cars: 3

Cooling water: 20t/h

Carbon molecular sieve nitrogen machine parameters

Sunjiawan Mine

Nitrogen output (Nm3/h) 600 per unit, 1200 for two sets

Nitrogen purity (%) 98

Outlet pressure (Mpa) 0.5 ~ 0.65

Starting time (min) 30

Installed capacity (KW) 230

Wulong Coal Mine:

Nitrogen output (Nm3/h) 800 per unit, 1600 in total for two sets

Nitrogen purity (%) 98

Outlet pressure (Mpa) 0.65 ~ 0.75

Starting time (min) 30

Installed capacity (KW) 250

Friction resistance calculation formula

• H=9.8×10-6×Q2WL/KD5--------------- (1)

• Where: H------ friction resistance loss Pa along the pipeline;

• L------ Pipe length, m;

• W------ Density ratio of nitrogen to air, 0.9672;

• Q------ nitrogen flow rate, m3/h;

• D------ Inner diameter of nitrogen pipe, cm;

• K------ pipe coefficient, 0.1180Mpa(3 inch pipe).

• ② The local resistance is 10% of the resistance along the road



Whether the diameter of the nitrogen transport pipeline meets the requirements of nitrogen transport checking formula

• D=145.7(Qmax/v) --------------②

• Where: Qmax-- maximum nitrogen transport flow, m3/min

• D-- Minimum diameter of nitrogen injection pipe, mm;

• v-- -- The allowable nitrogen flow rate in the pipeline is 20m/s

Nitrogen fire protection parameters

• ① Nitrogen fire purity: According to the coal mine safety regulations, the purity of nitrogen in the goaf fire injection is ≥97%.

• ② Nitrogen fire extinguishing purity: According to the laboratory investigation of Chongqing Coal Research Institute, the open fire in the fire area can still smoulder when the O2 content is 3%, so the nitrogen injected into the fire area should be high purity, according to the characteristics of the pressure swing adsorption nitrogen machine can not produce high-purity nitrogen, the purity of the fire extinguishing nitrogen is ≥98.5%.

• ③ Fire inerting index of goaf oxidation zone: According to coal mine safety regulations, fire inerting index of goaf oxidation zone is O2≤7%.

• ④ Nitrogen injection inerting index in the fire area: O2≤3% in the inlet air seal (when nitrogen is stopped), O2≤2% in the return air seal.

Nitrogen injection flow rate for fire prevention
(by ton of coal)

• Where: QN - nitrogen injection flow, m3/h;

• A - Annual production, mt/ year;

• 5 - According to domestic and foreign experience, the fire protection nitrogen injection flow per 1t of coal is 5m3;

• K - nitrogen injection fire protection coefficient, 1 ~ 2,

• C - The recovery rate of the working face is 0.85

Calculated according to the content of oxidized zone in goaf

• In the formula: Q0 - Air leakage in the goaf oxidation zone, according to 1/100 of the air volume of the working face,

• C1 - The average oxygen content of oxidation zone in the goaf is 15%;

• C2 - fire inerting index of goaf oxidation zone, which is 7%;

• Cn - when injecting nitrogen for fire prevention, the purity of nitrogen is 98%;

• K - The nitrogen transmission coefficient of the pipeline is 1.1





Nitrogen injection flow rate for fire suppression

• Formula: QN - nitrogen injection amount for fire extinguishing;

• V0 - fire area volume;

• C1 - the original oxygen content of the fire area, according to practical experience, is 6 ~ 8%;

• C2 - the oxygen content inerting index of nitrogen injection for fire extinguishing is 2.5%, and the fire area volume Q0 is calculated according to the following formula:

• V0= (a+b+c) s·h

• Formula: a - Width of stoping face, 7m;

• b - Width of gob cooling zone;

• c - width of oxidation zone in goaf;

• s - length of stoping face;

• h - mining height.

Nitrogen extinguishing diagram of fully mechanized caving surface in Liudaowan Coal mine, Xinjiang







Fire nitrogen injection timing

• a. When carbon monoxide appears in the corner of the working surface, its content increases upward, reaching 60ppm, nitrogen must be injected immediately; When its content fluctuates and changes, it only needs to reach 80ppm, and it must also be immediately injected with nitrogen fire prevention.

• b. When the work does not reach a reasonable degree of fire prevention advance during the mining process, nitrogen must be injected in time until the working face advance is greater than or equal to the reasonable degree of fire prevention advance to stop nitrogen.

• c. When the temperature at the temperature measuring site of the working face appears in the following situations, nitrogen must be injected into the fire prevention immediately: (1) The temperature at the temperature measuring site is 10℃ higher than the air inlet temperature; (2) The coal discharge temperature is higher than 35℃.

• d. When the shelf is withdrawn, regardless of whether there is a warning sign on the working face, nitrogen should be injected into fire prevention in time.

• e. When the high temperature coal is put into the goaf in the roadway, nitrogen must be injected immediately until the high temperature coal is used in the stifling zone.

Minimum nitrogen injection time

• QN - Nitrogen injection amount of oxidized zone in inactive goaf;

• V0 - goaf oxidation zone volume;

• C1 -- the average oxidation content of oxidation zone in goaf is 15%;

• C2 - fire inerting index of goaf oxidation zone, 7%;

• V0= oxidation zone width x working face length x mining height







Nitrogen injection foam process diagram





Foaming effect of foam solution with different flow rate during nitrogen foam injection

Nitrogen flow rate

Nitrogen pressure

Foam solution flow (L/h)

Foaming effect

250m3/h

0.4 MPa

200

Full foaming

300

Full foaming

350

Full foaming

400

Some of the foam solution is unfoamed