DL/T 435-2004Code for the prevention of pulverized coal firing furnace explosions/implosions in power plant boilers (English PDF)

Foreword

According to the Document Zong Ke Jiao [1998] No.18 issued by the previous

Ministry of Power Industry "Notice on issuing the Development and Revision Plan of

Professional Power Standards", this Code is revised based on DL 435-1991 "Code for

Prevention of Pulverized Coal Firing Boiler Firebox Explosion/implosions in Thermal

Power Plant".

There have been some significant changes in this Code over its previous editions in

the following technical aspects.

- MODIFY specified value of the furnace structural design pressure;

- ADD terms;

- ADD content on preventing furnace implosions;

- MAKE new supplement on the provisions of relevant equipment and their system

requirements as well as the running operations;

- ADD Informative Appendix "Reasons that may cause furnace explosion"

(Appendix A);

- ADD Informative Appendix "Explanation on the transient state pressure-bearing

capability designed for the furnace" (Appendix B);

- ADD normative appendix "Fuel trip time delay and additional alarm items"

(Appendix C).

This Code replaces DL 435-1991 since its implementation.

Appendix A and Appendix B of this Code are informative.

Appendix C of this Code is normative.

This Code was proposed by China Electricity Council.

This Code shall be under the jurisdiction and under the explanation of Technical

Committee for Standardization on Professional Power Plant Boilers.

This Code was drafted by Thermal Power Research Institute.

This Code was mainly prepared by Zheng Zemin, Gao Hanxiang, Yuan Ying and Xu

Chuankai.

This Code was first-time issued on September 18, 1991.

Code for the Prevention of Pulverized Coal Firing

Furnace Explosion/Implosions in Power Plant Boilers

1 Scope

This Code specifies basic requirements on relevant equipment and system aspects

for prevention of pulverized coal firing furnace explosions/implosions in power plant

boilers, shows out guide for the on/off sequence and operation of equipment.

This Code is applicable to pulverized coal firing furnace in power plant boiler.

2 Terms

For the purposes of this Standard, the following terms apply.

2.1

main primary air shut off gate

It is a kind of main air gate which can be closed tightly and prevent the primary air

entering the burners; generally, it shall be mounted on the pulverized coal-free airflow,

such as primary air fan outlet of positive pressure direct-blow pulverized-coal system

or coal pulverizer inlet of negative pressure direct-blow pulverized-coal system and

storage pulverized-coal system.

2.2

flame detector

The equipment to detect the flame-free and provide signal.

2.3

directional blocking

A sort of interlock system moves to the likely-to-be enlarged deviation direction and all

the relevant final control elements must be prohibited when the furnace pressure is

tested to deviate from the normal value significantly.

2.4

fan test block capability

2.11

ignitor

It can provide adequate ignition energy for igniting the permanent devices (including

sparker, igniting oil and popgun) of the main burner fuel for an instant. The capacity of

the ignitor as close relationship with the fire behavior of the main fuel, burner type and

requirement for the ignitor function, generally, it consists of Class-I and Class-II

ignitors.

Class-I ignitor. used to ignite the gas-pulverizer mixture entering the furnace from the

main burner in any operating condition. This type of ignitor requires large capacity;

generally, it shall be over 20% of the heat quantity of the main burner under full-load.

Class-II ignitor. can only be used to ignite the gas-pulverizer mixture entering the

furnace from the main burner according to the air volume and pulverized coal volume

when igniting, its capacity is generally 10%~20% of the heat quantity of the main

burner under full-load.

The above two ignitors are both be used for combustion-supporting under low-load or

when the burning is instable, however, it may not be used as means for saving

extinguishment when the furnace has been fire-extinguishing but not yet been purged

according to the requirements.

2.12

warm-up oil gun

It is the oil gun for warming up boiler, lifting pressure, washing pipe and with low-load,

while its thermal power hereof is larger than that of the ignitor (usually, its total thermal

power is about 30% of the thermal power for the full-loaded boiler).

2.13

furnace safety supervisory system ("FSSS" for short)

It is a kind of security protection and sequential control equipment that ensures that

the equipment of the boiler combustion system is safety on/off according to the

specified working order and conditions, and that can rapidly cut off all the fuel

(including igniting fuel) entering the furnace in critical operating conditions, so as to

prevent destructive emergencies like deflagration and explosions.

Note. The primary functions of the international so-called "burner management system", "fuel-firing safety

system" or "burner control system" are identical to FSSS defined by this Code.

2.14

logic portion

stable flame

In the range of operation, and in the process of changing the load with the specified

maximal variable rate, the boiler may maintain its stable-burning flame continuously.

2.21

burner

The equipment supplies the fuel and air into the furnace according to the required

velocity, turbulence and concentration, and makes the fuel be on fire and burnt stably

in the furnace.

2.22

burner shutoff damper

The shutoff damper loaded in front of the burners, used to shutoff the fuel-air mixture

entering the main burner.

2.23

combustion control system

Self-control the fuel and air flow and furnace pressure entering the furnace, so as to

make the boiler maintain proper air -fuel-ratio in the specified load range, and ensure

the flame stabilization and favorable fuel combustion governing system in the boiler,

as well as maintain the furnace pressure in the prescribed range.

2.24

pulverized coal firing furnace purge

Purge the boiler furnace with blowing fan and induced draft fan in constant mass air

flow when the boiler load is no less than 25% and not more than 40% of the boiler

full-load, while the time depends on the larger value between the following two.

a) No less than 5min;

b) Make 5 times of air change for the furnace and space of its backside

pressure-containing members.

2.25

furnace explosions

Pulverized coal, oil mist, fuel and air mixture is accumulated in the furnace or the

restricted clearance of the backside flue attached to the furnace; when the

concentration of these mixtures is within the deflagration limit range, it may deflagrate

judgments, and to avoid the unsafe operating conditions.