Natural Gas Fired Box Type Heat Treatment Furnace Energy Saving

Natural Gas Fired Box Type Heat Treatment Furnace

1. Equipment Purpose

RX3-600-9 gas furnace is mainly used for heat treatment of various steel workpieces,

alloy parts and castings at a certain temperature.

2. Technical Parameters

3.The overall characteristics and structure of the equipment

3.1 Introduction to each structure

3.1.1 Furnace body​

3.1.1.1 Furnace steel frame

The furnace body is composed of furnace frames on both sides: welded with channel steel and plate steel.

The side and rear columns made of steel are pulled together to form a sturdy steel frame structure that is strong,

durable and reliable. The furnace body has a straight and good appearance. It's painted with two coats of

primer and two coats of topcoat as per standards, with key parts in high temperature resistant paint.

14mm thick plates are installed around the furnace mouth by bolts to avoid deformation at high temperature.

Anti-slip platforms and escalators are set properly for component operation and maintenance,

meeting relevant national standards.

3.1.1.2 Furnace lining

1260 high-purity refractory fiber folded blocks with a 1000℃ long-term use temperature have multiple

advantages like low thermal conductivity, light bulk density, good insulation, easy construction and long service life.

They can cut storage and heat dissipation losses of furnace lining and save energy.

It uses a composite large module combined structure and stainless steel round steel fixing technology.

For the furnace lining's high temperature section, a refractory layer with 300mm aluminum silicate fiber

compression block plus 50mm insulation section (total 350mm thick) is adopted. The stacked structure

fiber is perpendicular to the heating surface, has small shrinkage under high temperature and good high

temperature and air flow scouring performance. This method is widely used in similar furnaces with good

results and long furnace lining service life.

3.1.1.3 Furnace bottom

The heat-resistant insulation layer has a three-layer structure with two materials.

The upper layer uses refractory high-alumina bricks for pressure-bearing in workpiece heat treatment,

while the middle and lower layers use lightweight clay bricks for heat insulation.

Sealing is vital in furnace design due to its impacts on multiple aspects,

and a good sealing solution is required considering the harsh environment.

The sealing among the furnace door, furnace body and trolley is key,

with the furnace door and body sealed by an electric push rod pressing the closed door to prevent hot air leakage.

3.1.1.4 Furnace door

The furnace door is composed of a fiber lining made of aluminum silicate fiber folding blocks and

a steel structure shell, being strong and long-lasting. Its frame is of large channel steel and welded

to pre-embedded steel plates on the foundation. It's driven vertically by an electric hoist with pulleys

and chains, avoiding the need for a pit. There's a soft-hard contact sealing structure where a cylinder

mechanism presses it for sealing when closed and creates a gap when opened to ensure smooth movement.

The method is simple, practical, with reliable sealing and convenient maintenance,

and the furnace door has its own structural characteristics.

3.1.2 Combustion system

Combustion system

The combustion system includes a new type of high-speed burner made in China following

German Krom Technology, along with a proportional combustion control system, gas valve,

solenoid valve and burner control box. The burner has automatic ignition, flame monitoring,

flameout alarm and pre-ignition purge functions. The actuator controls the burner's size based

on the heat load demand after receiving the temperature control instrument's signal to

adjust the furnace temperature.

3.1.2.1 The burner has an adjustment function, the combustion capacity adjustment ratio can reach 1:10 ,

and the air coefficient range is 1 to 5. Therefore, the uniformity of the furnace temperature

in different temperature sections can be effectively adjusted according to the process requirements,

and the process requirements and various thermal systems of the furnace can be met.

The air-fuel ratio can be effectively controlled to save fuel while achieving complete combustion.

3.1.2.2 When the gas trolley type heating furnace is working, in case of power failure detected

by the monitoring or safety alarm system, the burner electric gas valve and main pipe safety

valve will be automatically cut off. After power restoration, the main pipe safety valve needs

manual confirmation to start, and ignition procedure starts after normal purging.

The burner has a control unit centered on a proportional control system, enabling automatic

control of the whole process like ignition, alternating between high and low fire, flameout alarm

and re-ignition. The burner control box allows for manual/automatic switching without interruption.

Operators can operate in front of the furnace or on the instrument cabinet to adjust and control

burner combustion state, and connecting it with the control system realizes closed-loop control

of the whole furnace temperature and fuel combustion, making the operation more user-friendly.

3.1.2.3 The pipeline in front of the burner is equipped with an automatic control natural gas ball valve,

a solenoid valve and a manual gas regulating valve, which can realize the reasonable proportion of

natural gas and combustion hot air supply, so that the excess air coefficient is controlled below 1.1 ,

thereby improving the combustion quality and ensuring that the burner works under normal process requirements.

3.1.2.4 A new type of burner with good adjustment performance is adopted based on the user's

process curve and furnace temperature uniformity requirements. It uses large and small fires and

hot air for combustion assistance to raise the initial temperature of fuel gas, improving furnace

thermal efficiency and meeting heat treatment process needs.

The combustion system has these features:

• It simplifies and makes reliable the temperature control system's hardware and software,

saving software programming and debugging time.

• The burner has optimal combustion with low pollution emissions as it can do large and

small fire heating, reducing emissions and saving energy.

The pipeline (air supply, gas supply) system:

• Air supply system: The combustion-supporting air pipeline includes a high-pressure centrifugal fan,

an automatic regulating valve, a pressure measuring device and pipelines. It matches gas to control

the air excess coefficient below 1.20. The blower meets national standards with a noise

level ≤ 85db at 1.5 meters away and has a shock-absorbing device at its base.

3.1.3 Gas supply system

The natural gas main is equipped with a pressure regulating device, filter, high-pressure switch,

low-pressure switch, and pressure gauge. The automatic regulating valves for controlling large

and small fires in the separate pipelines use actuators to control large and small fires. For safety,

a safety quick shut-off valve is installed on the natural gas main.

3.1.4 Smoke exhaust system

Direct exhaust is adopted to discharge the flue gas outside the factory through the furnace pressure control,

through the flue damper and the flue. The flue gas heats the cold air entering the heat exchanger

through the heat exchanger, thereby achieving the purpose of improving the thermal efficiency of the furnace.

The design dimensions of the flue and heat exchanger are considered when the fuel is natural gas.

A rain cap is installed on the top of the chimney. The emission of flue gas meets the second-level

standard of the national standard GB19297-1996 "Comprehensive Emission Standard of Air Pollutants",

and the service life of the chimney is ≥15 years.

3.1.5 Furnace pressure control system

Maintaining the furnace work surface pressure at ±200Pa benefits temperature uniformity and thermal efficiency.

High furnace pressure leads to hot air escaping, causing heat loss and affecting the lifespan of related parts.

Low furnace pressure lets cold air in, increasing heat loss and causing issues like secondary combustion

and affecting temperature uniformity and workpiece oxidation.

For fully automatic control furnaces, effective technical measures are needed to control furnace pressure.

The adopted method uses a system with pressure taking devices, pressure transmitters and intelligent

instruments to control the pressure at an optimal state (trolley surface at slightly positive pressure),

achieving a dynamic equilibrium in smoke exhaust volume to save energy and maximize furnace efficiency.

The rear exhaust method is employed with a flue set at the back of the furnace, connected to a heat

exchanger in line with GB3486-83 and led to the outside.

3.1.6 Fault detection and alarm system:

The heat treatment furnace is equipped with complete fault detection, alarm, diagnosis and

safety protection functions. Various fault displays use fault alarm modules,

and there is a light alarm on the control cabinet.

3.1.7 Control system

The control system is designed and made with advanced and mature international technologies,

using stable and reliable instruments and equipment, featuring high stability, reliability, strong

anti-interference ability, and ensuring real-time and accurate monitoring during the heat treatment

furnace's normal operation. It's also simple to operate, easy to maintain, practical, expandable,

and has accurate measurement.

The overall control system solution includes:

• Control system and information transmission involving combustion, power and temperature

control systems which handle production processes like furnace loading, unloading, heating

and perform functions related to setting and collecting process and operating parameters and data.

• The combustion control system is crucial for a furnace as its configuration impacts temperature

control accuracy, uniformity and combustion efficiency (affecting product quality and energy consumption).

For its process, the mV signal from the K-type thermocouple is sent to the Japanese Shimaden

temperature PID controller. After calculation, the 4 - 20mADC control signal is transmitted to the

electric actuator and then converted into a signal to control the burner controller with German

technology which controls burner ignition and flame monitoring and has specific steps

when flame signals aren't detected.

4. Environmental and energy-saving protection requirements

Since the fuel used is low-pollution fuel, the combustion adopts high-speed burner,

and the air-fuel ratio and various pressures are automatically adjusted to ensure that

the fuel combustion is fully stable, and the generation of incomplete combustion products

such as carbon particles and CO is fundamentally eliminated. At the same time,

the flue gas is discharged from high altitude using 15m smoke. Therefore,

the blackness can be at Level 0 of the Ringelmann scale. The SO2 emission and ground

concentration as well as the NOx emission are all lower than the national standard-GB16297-1996 "

Comprehensive Emission Standard of Air Pollutants".

Among the technical measures adopted:

All-fiber furnace wall structure

Direct flame automatic burner

Temperature automatic control system

Automatic control of wind pressure, furnace pressure, natural gas pressure and air-fuel ratio

Furnace body full refractory fiber sealing structure

Flue gas waste heat recovery, i.e. preheating of combustion air and heat preservation of hot air pipes

The energy consumption is greatly reduced, reaching the first-class furnace standard in ZBJ01004-87 "

Energy Consumption Classification of Heat Treatment Furnaces". That is, the energy consumption per

ton of workpiece is less than 70kg of standard coal, and the thermal efficiency is more than three times

higher than that of bricks. At the same time, the surface temperature of the side wall of the furnace can be less than 60℃.

Corresponding national standards:

Products designed and manufactured with domestic technology shall be designed, manufactured

and inspected in accordance with the corresponding national standards, industry standards or

enterprise standards. The standards are as follows:

1.In terms of reasonable optimization design and reduction of various heat losses,

it complies with the "Principles of Enterprise Rational Heat Use Technology Management" stipulated

in GB/T3486-93 to achieve the requirements of high quality, high yield, energy saving and environmental protection;

2.The masonry and installation of refractory materials shall comply with GB50211-2004 "

Industrial Furnace Masonry Engineering Construction and Acceptance Specification";

3.The noise level complies with the workshop requirements in GBJ87-85 "Noise Standards

for Various Locations in Factory and Enterprise Plant Areas";

4.Environmental pollution emissions meet the Class I standard in GB3095-1996;

5.The temperature of the effective heating zone of the furnace is measured according to GB/T9452-2003,

and the temperature uniformity is ±10℃;

6.The energy consumption level reaches the special furnace level specified in ZBJG1004-87 "Energy

Consumption Classification of Heat Treatment Furnaces";

7.The main material standards for the furnace body are: heat-resistant steel for the guard plate of

the furnace car and the furnace pad (GB/T8492-87), heat-resistant steel plate (GB4238-92 ) ,

clay refractory brick (YB/T5106-1993 ) , amorphous refractory material (GB4513-84 ) ,

clay and high-alumina refractory castable (YB/T5083-1997);

8.GB985-86 "Basic forms and dimensions of manual arc welding joints";

9.JB/ZQ4000.3-86 "General Technical Requirements for Welding Parts";

10.GB/T5000.9-1998 "General Technical Requirements for Chip Machined Parts";

11.GB/T1804-1992 "Tolerances of shape and position, general tolerances and unspecified

tolerances of linear dimensions";

12.GB1801-79 "Tolerance and fit dimensions up to 500mm hole, shaft tolerance zone and fit";

GB/T1801-1999 basic dimensions up to 500mm preferred common fit limit clearance and limit interference;

13.GB8923-1998 "Surface rust grade and rust removal grade of steel before painting";

GB/T1182-96 Symbols and standards for geometric tolerances;

14.JB/T13384-21992 "General Technical Requirements for Packaging";

15.GBJ55-1983 "Design Specifications for Power Installations for Industrial and Civil General Equipment";

16.GB420-1984 "Electrical control equipment, part 1, low voltage electrical appliances and electronic control equipment".

5. Models and origins of main purchased parts

5.1Mechanical part

5.2 Control system

6. Supply Scope

7.Quotation

8.Post-sales Service

The furnace is warranted for 13 months starting from the date of shipment. In the warranty period,

damages are repaired or replaced if they are caused due to manufacture defects.

The buyer is charged at a certain rate if the damages are caused by the buyer itself.