DL/T 435-2018 in English

DL/T 435-2018 Code for the prevention of furnace explosions/implosions in power plant boilers

1 Scope

This standard specifies the technical requirements for the design, installation, commissioning, operation, and maintenance of power plant boiler furnaces to prevent explosions and implosions.

This standard is applicable to power plant boilers with pulverized coal, oil and gas as fuel.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

GB 50041 Standard for design of boiler plant
GB 50049 Code for design of small fossil fired power plant
GB 50058 Code for design of electrical installations in explosive atmospheres
GB 50251 Code for design of gas transmission pipeline engineering
GB 50253 Code for design of oil transportation pipeline engineering
GB 50660 Code for design of fossil fired power plant
DL/T 335 Operation specification for SCR flue gas denitrification system in fossil-fuel power plant
DL/T 466 Guide of type selection of pulverizers and pulverizing systems for power station
DL/T 611 Operating guide for 300MW~600MW coal boiler
DL/T 748.4 Guide of maintenance of boiler unit for thermal power station - Part 4: The maintenance of pulverized coal system
DL/T 748.5 Guide of maintenance of boiler unit for thermal power station - Part 5: The maintenance of air & flue system
DL/T 831 Guide on selection of furnace characteristic parameters for large pulverized coal fired boilers
DL/T 852 Guide of boiler start-up commissioning
DL/T 1091 Code of furnace safeguard supervisory system for thermal power plant
DL/T 1127 Guide for design and operation of plasma ignition system
DL/T 1316 Design and operation guidance for less oil ignition system of pulverized coal fired boiler in thermal power plant
DL/T 1445 Technical guidelines of burning blended coal in pulverized coal fired power plant boilers
DL/T 1683 Guide of operating for 1000MW grade supercritical unit
DL/T 5121 Technical code for design of thermal power plant air & flue gas ducts/ raw coal & pulverized coal piping
DL/T 5145 Technical code for design and calculations of coal pulverizing system of fossil-fired power plant
DL/T 5203 Technical code for explosion prevention design of coal and pulverized coal preparation system of fossil-fired power plant
DL/T 5204 Code for design of oil / gas piping of power plant
DL/T 5240 Technical code for design and calculation of combustion system of fossil-fired power plant
DL/T 5428 Technical code for design of I&C protection system in fossil fuel power plant
DL/T 5550 Code for design of fuel oil system for fossil-fired power plant

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1
furnace explosions
phenomenon where a mixture of coal powder, oil mist, gas and air accumulates in the confined space of the furnace or the rear flue connected to the furnace. When the concentration of these mixtures is within the limit range of deflagration, they will deflagrate when encountering an ignition source. The temperature of the combustion products will increase sharply, the volume will expand, the pressure will instantly increase, and even the furnace will be damaged. The more volatile matter precipitates in pulverized coal and the finer the pulverized coal is, the greater the pressure generated by the explosion of pulverized coal suspended in air. As long as the concentration of the pulverized coal/air mixture reaches 0.05 kg/m3, an explosive mixture can be formed. The mixture with a concentration of 0.3 kg/m3 to 0.6 kg/m3 is most prone to explosion. See Annex A for possible causes of furnace explosions.

3.2
furnace implosions
phenomenon where the pressure difference between the inside and outside of the furnace wall exceeds the pressure borne by the furnace wall due to excessive negative pressure in the furnace, resulting in the furnace wall bursting inward See Annex A for possible causes of furnace implosions.

3.3
boiler furnace explosion pressure
transient pressure under abnormal conditions that the furnace structure can withstand, i.e., the limit value of the transient pressure that the furnace can withstand in a short period of time, which is also the transient design pressure of the furnace

3.4
boiler furnace design pressure
pressure obtained by dividing the design transient pressure of the furnace implosion prevention by a safety factor (the safety factor when the basic allowable stress of the material is determined according to the yield limit), namely:

(1)

where,

pF, ds——the boiler furnace design pressure, kPa;

pF, mft——the transient explosion pressure of the furnace at the time of the master fuel trip (MFT) of the boiler, kPa;

ns——the safety factor of the material when the basic allowable stress is determined according to the yield limit, which is taken as 1.67.

3.5
primary air shutoff damper (valve)
damper (valve) used to tightly block the flow of air, usually mounted in front of a primary air control damper

3.6
primary air control damper (valve)
control damper (valve) that regulates the air volume of primary fans or coal pulverizers

3.7
safety shutoff valve; safety trip valve
quick shutoff valve that automatically and completely shuts down gaseous or liquid fuel to the master burner or ignitor in response to a normal or safe trip command

3.8
coal pulverizer outlet maximum temperature
maximum outlet temperature of the coal pulverizer determined according to the explosion prevention and allowable temperature conditions of the coal pulverizer, which is related to factors such as the type of the coal pulverizer, the characteristics of the coal quality, and the composition of the drying medium. For the middle storage pulverizing system of steel ball coal pulverizer, it generally refers to the medium temperature at the outlet of the coal pulverizer; for direct-fired pulverizing systems such as double-inlet and double-outlet ball pulverizers, medium-speed pulverizers, and fan pulverizers, it generally refers to the medium temperature at the outlet of the pulverized coal separator

Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Basic requirements
5 Equipment and corresponding system requirements
6 Furnace implosion prevention protection (balanced draft boiler)
7 Coal-fired system
8 Oil system
9 Gas system
Annex A (Informative) Possible causes of furnace explosions
Annex B (Informative) Description of the transient design pressure capacity of the furnace
)