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DL/T 435-2004

Chinese Standard: 'DL/T 435-2004'
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Standard ID DL/T 435-2004 (DL/T435-2004)
Description (Translated English) Code for the prevention of pulverized coal firing furnace explosions/implosions in power plant boilers
Sector / Industry Electricity & Power Industry Standard (Recommended)
Classification of Chinese Standard F23
Classification of International Standard 27.100
Word Count Estimation 26,219
Date of Issue 2004-03-09
Date of Implementation 2004-06-01
Older Standard (superseded by this standard) DL/T 435-1991
Drafting Organization National Electric Power Research Institute
Administrative Organization Power industry boiler Standardization Technical Committee
Regulation (derived from) National Development and Reform Commission Notice 2004 No. 16
Summary This standard specifies the outside to prevent the pulverized coal power plant boiler furnace explosion/implosion equipment and systems in the relevant basic requirements, given the equipment start and stop the operation of the order and operation guide. This standard applies to pulverized coal power plant boilers.

DL/T 435-2004
ICS 27.100
F 23
Recording number. 13556-2004
Replacing DL/T 435-1991
Code for the Prevention of Pulverized Coal Firing
Furnace Explosion/Implosions in Power Plant Boilers
Issued by. National Development and Reform Commission
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Terms ... 4 
3 Relevant Requirements on the Prevention of Furnace Explosions ... 9 
Appendix A ... 44 
Appendix B ... 46 
Appendix C ... 47 
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
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.
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.
flame detector
The equipment to detect the flame-free and provide signal.
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.
fan test block capability
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
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.
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).
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.
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.
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.
burner shutoff damper
The shutoff damper loaded in front of the burners, used to shutoff the fuel-air mixture
entering the main burner.
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.
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.
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.
3.2 Requirements on the Corresponding System of the Equipment
3.2.1 Structural design of the furnace
The structural design of the furnace requires.
a) The furnace structure shall be able to bear transient pressure emergent in
improper conditions; under this pressure, the furnace shall not bend or yield by
any supporting parts, which may result in the permanent deformation.
b) The design transient pressure of the furnace shall not be less than ±8.7kPa
(related explanation refers to Appendix B).
Note. For the boiler with capacity of 4000h (equivalent to boiler of 100MW unit) or below, the
absolute value for the design transient pressure of the furnace may be less than 8.7kPa, but it
should not be less than 6.7kPa.
c) Whatever the reasons, when the fan test block capability exceeds -8.7kPa, the
design transient negative pressure of the furna......
Related standard: DL/T 435-2018    DL/T 425-2015
Related PDF sample: DL/T 805.4-2016