Outline of Industrial Combustion Systems
If the heat required in an industrial furnace or process is to be provided by the combustion of a fuel such as gas, a whole combustion system needs to be designed. In addition to technical requirements, standards such as EN 746-2 and ISO 13577-2 must be complied with for safety. During design, the process, i.e. the work, plays a crucial role in shaping the heating system. For this purpose, the process should be analyzed under the following main headings.
Process temperature
Low temperature (<600 °C). Ex. Food and paint drying Medium temperature (600-1050 °C). Ex. Metal stress relieving, hardening High temperature (1050-1250 °C). Ex. Steel annealing Very high temperature (> 1250 °C). For example. Glass melting, technical ceramic firing Plant and burner capacity, type and number of burners
Mode of operation of the process: continuous or batch
Heating mode: indirect or direct
Furnace atmosphere: oxidative (oxidizing) or reductive (reducing)
Combustion air temperature: ambient air, heated air
The industrial gas combustion plants that emerge from the elucidation of these issues consist of four parts designed according to the requirements of the process as a whole.
Gas Inlet Line Air
Inlet Line Burner
Control Line
Process Control System
Gas Inlet Line
These lines are needed to reduce the gas pressure coming into the facility to the working pressure of the burners and devices, to secure the gas, and to measure the amount consumed. The main components of a classical line manufactured in accordance with EN 746-2 are as follows;
| Pose | Sample Device | 746-2 Attribution | Recommendation |
|---|---|---|---|
| 010 | AKT Ball Valve | 5.2.2.1 | |
| 020 | GFK Gas Filter | 5.2.2.2 | The selected filter must not cause a pressure loss of more than 10 mbar at maximum flow rate |
| 030 | DH Manometer tap | 5.2.2.1 | The pressure gauge tap reduces the pressure to which the pressure gauge is exposed after measurement and separates the pressure gauge from the line pressure. |
| 040 | KFM Manometer | ||
| 050 | JSAV Safety Shutoff Valve | 5.2.2.4 | If selected in the same diameter as the regulator, there is no need for reduction in the pipe. |
| 060 | VGBF Regulator | 5.2.2.4 | The regulator is designed for the smallest possible size and for convenient control, input and output TR selection should be made so that the entire pressure difference range is used. |
| 070 | AKT Ball Valve | 5.2.1.15 | To prevent unauthorized intervention, the valve handle can be removed. |
| 080 | VSBV Safety Escape Valve | 5.2.2.4 | The safety relief valve prevents unnecessary activation of the safety shut-off valve by reducing the sudden pressure rise in the line up to a certain level. |
| 090 | DM, DE Debi Metre | ||
| 100 | DG Pressostat (Gas Min.) | 5.2.2.5.2.1 | The min. value to be set depends on the installation position and the process. |
| 110 | DG Pressostat (Gas Max.) | 5.2.2.5.2.2 | The valves must be mounted with the membranes horizontal or vertical and the breather holes must be kept free from dirt and moisture. The max. value to be set depends on the installation position and the process |
| 120 | VAS Magnetic Valve (Magnetic valve) | 5.2.2.3 | |
| 130 | DG Pressostat | For leak tightness check, it is recommended to set the presostat to half the inlet pressure. | |
| 140 | TC Tightness Check | 5.2.2.3.4 | EN 746-2 requires leak tightness control for capacities of 1200 kW and above, and recommends it below 1200 kW. |
Function Description
When the main ball valve (010) is open, the regulator (060) sets the required gas pressure for the combustion system. Any possible dirt from the line or gas is filtered out by the filter (020). If the gas regulator creates an incorrect outlet mpressure (e.g. membrane rupture), the gas is shut off by the safety shut-off valve (050). Safety escape valve (080) prevents unnecessary activation of the safety shut-off valve by discharging gases that may escape from the safety shut-off valve and reducing the line pressure in temporary pressure fluctuations. Thus, the continuity of the plant is ensured.
Magnetic valves (120), low and high pressure switches (100/110) and the leakage control device (140) are parts of the safety system. They are activated via the process control system. In case of insufficient or too high gas pressure, the process control receives a signal and closes both valves to secure the gas. After each start-up or shutdown of the system, the leak tester (140) checks the valves (120).
The amount of gas consumed can be read from the flow meter (090) and the inlet and outlet pressures can be monitored by manometers (030/040).
For optimal adjustment of the gas pressure regulator, safety shut-off valve and safety escape valve, the switch-on, switch-off and tolerance groups of the devices must be taken into account. In order to avoid overlapping setting values due to tolerances, it is recommended to create a pressure step diagram.
Air Inlet Line
Most industrial burners operate at pressures higher than atmospheric pressure. Air inlet lines are needed to supply and control the air to the burners with a central fan. The main components of a conventional line manufactured according to EN 746-2 are as follows.
| Pose | Sample Device | 746-2 Attribution | Recommendation |
|---|---|---|---|
| 010 | Fan and air intake filter | It is recommended to use a filter in front of the fan | |
| 020 | KFM Manometer | ||
| 030 | DH Manometer tap | ||
| 040 | DG Pressostat | 5.2.2.5.1 Air | Air min. presostat |
| 050 | DG Pressostat | 5.2.2.5.1 Air | Differential pressure switch to control the air flow. |
| 060 | VMO Measurement Orifice | Differential pressure switch to create differential pressure during flow. |
Function Description
The air pressure generated by the fan (010) is controlled by the air min. is monitored by the air min. switch (040). Following the start of the fan, the process control monitors the switching of the switching of the switch by the process
control.
During pre-sweeping, the differential pressure switch (050) and orifice (060) monitor the presence of air flow. Air min. Or TR If the differential pressure falls below the specified value, the system switches to fault lockout.
746 – 2 requires a check to be made on the inlet filter of the fan. his can be done using a differential pressure switch to be installed on the filter or a pressure switch to be installed on the outlet side of the fan. The filter check gives a warning signal, but this signal does not have to be included in the safety chain.
For many plants, it is recommended that the intake air for the fan is drawn from outside the plant building (open air). This will reduce the need for maintenance of the filters, but the fact that the air is drawn from outside does not eliminate the need for filters.
Burner Control Line
In order to design the burner control lines, it is necessary to have decided on the following issues.
- Capacity control
- Modulation
- Stepped control
- Pulse firing
- Air/gas ratio
- Mechanical
- proportional
- Pneumatic proportional (equal pressure
regulation) Electronic proportional
- Flame monitoring and burner fault behavior
- Ionization controlled
- UV controlled
- Control over inferno temperature
- Number of burners and zones
- Single burner
- Multi-burner, single zone
- Multi-burner, multi-zone
- Combustion air temperature
- Ambient air (Cold air combustion)
- Hot air, central recuperation
- Hot air, self recuperation
- Hot air, regeneration
- Combustion ignition
- Direct ignition
- Ignition via pilot
- Self-ignition in a hot furnace
According to the necessity of the process, choices are made on the above issues. In addition to these, issues such as flameless combustion to reduce NOx gases, oxygen trimming to reduce scale, dual fuel, premix combustion can also be among the issues to be decided according to the process.
As an example, a single burner, cold air, direct ignition, pneumatic proportional, ionization controlled system is described.
| Pose | Sample Device | 746-2 Attribution | Recommendation |
|---|---|---|---|
| 010 | VAS Solenoid Valve | 5.2.2.3.2 | |
| 020 | GIK Equal Pressure Regulator | 5.2.3.3 | Regülatör mümkün olan en küçük boy ve optimal bir kontrol için, giriş çıkış basınç fark aralığının tamamı kullanılır şekilde seçim yapılmalıdır. |
| 030 | VCG Combination Valve (VAS Solenoid Valve + VAG Equal Pressure Regulator) as an alternative to GIK |
||
| 040 | GEHV, GEH Flow Regulating Valve | ||
| 050 | EKO Compensator | 5.2.1.5 | |
| 060 | BIO, ZIO, BIC, ZIC Burner | 5.2.5.1 | Burners can be equipped with a burner stone or ceramic barrel. Burner selection is made by considering parameters such as process, plant, capacity, temperature, flame form, flame speed, fuel type, insulation thickness. |
| 070 | BVA+IC Actuated regulating flapper | To make maximum use of the valve adjustment characteristic, The smallest possible flapper should be selected. Attention should be paid to the permeability of the flap in the closed position. | |
| 080 | BVA, DKR Throttle valve | All manually adjusted air regulating equipment in accordance with 746-2 must be fixed at the set points and secured against unauthorized intervention. | |
| 090 | BCU 370 Burner Control Unit | 5.2.6.1 | Unit with internal ignition transformer, mounted next to the burner for easy commissioning. |
Function Description
It is designed for processes such as ladle heating and aluminum melting that require a simple combustion system with high temperature control precision and low cost.
The capacity of the burner is adjusted infinitely via the air actuator (070), for example by means of an analog signal 4-20 mA. The pneumatic connection (020-030) adjusts the gas pressure proportionally to the air pressure and ensures that the air/gas ratio remains constant, while at the same time acting as a safety against air shortage. The regulating and throttling valves (040, 080) limit the air flow rate and allow the air/gas ratio to be adjusted.
Fluctuations in the internal pressure of the furnace do not change the air/gas ratio as they affect both gas and air flow rate at the same rate.
Burner ignition and flame monitoring is done by BCU 370 (090). The BCU 370 controls the fan and moves the control flap (090) to the pre-sweep and ignition positions. Following the pre-sweep, the burner ignition takes place and the process control system is allowed to adjust. The process control system then controls the capacity via the actuator (070) according to the capacity demand.
According to 746-2:2010, for burner capacities between 120-360 kW, ignition is only possible at low capacity (slow-opening gas valve).
The definition of pneumatic proportionality and the ignition position via the air adjustment damper (070) is considered equivalent to the use of an ignition by-pass valve as per 746-2:2010. The ignition position of the air adjustment damper (070) must be monitored by a limit switch or a pressure switch on the air side.
A capacity of up to 33% and a safety time of 3 seconds meet the requirements of the standard. If the burner capacity exceeds 1200 kW, the use of a tightness control device becomes mandatory. The BCU 370 does not perform the required lockout in case of a DG min error signal as specified by 746-2:2010.
Process Control System
A sample process control system including temperature control of a single burner system with ionization control, gas and air control is as follows.
| Poz | Örnek Cihaz | 746-2 Atıf |
|---|---|---|
| 010 | Feeding | |
| 210 | Combustion air fan | |
| 300 | Safety limitations | 5.2.2.3.1 |
| 311 | DG Air min. presostat | 5.2.2.5.1 |
| 321 | DG Gas min. switch | 5.2.2.5.2.1 |
| 322 | DG Gas max. switch | 5.2.2.4 |
| 331 | Emergency stop button | 5.2.2.3.1 |
| 332 | Temperature overshoot | 5.2.2.3.1 |
| 341 | Front sweep | 5.2.3.2 |
| 350 | TC 1-3 Tightness Check | 5.2.2.3.4 |
| 410 | Valve control | 5.2.2.5.2.2 |
| 450 | BCU 460 Burner Control Unit | 5.2.6.1 |
| 510 | Temperature control device |
Function Description
Electrical voltage is supplied to the control system via the supply (100). Air before the combustion fan (210) is started. Min (311) to check that the fan is in the stop position. The safety limits (300) control the safety-related signals air min. (311),
gas min. (321), gas max. (322), emergency stop (331) and temperature overshoot (332).
After the presence of the start signal and the check of all safety parameters (300), the tightness check (350) and the presweep (341) are started. After the end of the pre-sweep (341) and the arrow signal (350) of the tightness test, the safety chain is established (yellow), the burner is moved to the ignition position (410) and ignited. With the presence of the flame signal (450), the burner is operational. The temperature controller (510) can now check the capacity.
If even one of the safety measures goes out of bounds, if the sealing control (350) trips or if the burner controller (450) detects a fault, the system performs a fault shutdown. This shutdown can only be reset manually. The safety limits must be tailored to the needs of the process and the plant.
Burner ignition and flame monitoring is done by the BCU 460 (090). The BCU 460 controls the fan and moves the control flap (090) to the pre-sweep and ignition positions. Following the pre-sweep, the burner ignition takes place and the process control system is allowed to adjust. The process control system then controls the capacity via the actuator (070) according to the capacity demand.
The burner control unit (450) and the sealing controller (350) control the same automatic safety shut-off valves. BCU 460 is shown in the example. If another control unit is used, different signals may need to be processed. The start limit (LDS) of the control unit (450) must be realized by an additional control.
The information above is a guide and is subject to change. For the most accurate and up-to-date information, please use the docuthek website.
