c e t r A t n o i t p i r c s e D t c u d o r P
Gas Conditioning Tower
m . L . F Product Description
Technical Description Following for guidance only
Gas Conditioning Tower (GCT) Technical Description Object of GCT The object of the GCT is to condition and cool kiln gas before it is dedusted in an electrostatic precipitator (ESP). The cooling of the gas protects the ESP from high temperatures and the higher humidity of the gas increases the performance of the ESP. Furthermore, some of the dust in the kiln gas is separated from the gas by gravity in the GCT. An additional purpose of the GCT is to cool the flue gas before it enters a process fabric filter (FF)where very low temperatures can be required in order to protect the filter bags.
General description FLSmidth Airtech is continually optimising the concept of the GCT. One of the key features where FLSmidth Airtech differs from others is in the effort of creating a good gas distribution in the GCT.
Type A
Product Description
Type B
Two main types of Gas Conditioning towers are available. Type A with gas distribution by swirl and type B by grates. Both GCT types are for small to large gas flows i.e. 50 to 500 m 3/sec
FLSmidth Airtech supplies two different systems of water injection, one is a one phase flow back system. and the other a two phase system where water and compressed air are mixed. By using the two phase system, the droplets get smaller and the nozzles are exposed to less wear. The water injection is controlled by the thermodynamic system developed by FLSmidth Airtech. The thermodynamic control is faster and more exact than a traditional regulation system. Furthermore, it can automatically open and close lances according to the gas flow and temperature of the gas entering the tower. The water evaporates in the tower and thereby conditions the flue gas. The flue gas leaves the tower in the bottom where a hopper collects the dust separated by the gravity. The dust is removed by a dust transport system.
Gas Distribution For small to large gas flows i.e. 50 to 500 m 3/sec two main types A and B of GCT are available. FLSmidth Airtech is continually optimising the operation of the GCT. One of the essential features to optimise is the gas distribution inside the GCT. The development is based on model experiments, computer simulations with the CFD program and continuous evaluation of our own experience and that of our customers In the figure, Type A, the distribution in the tower is obtained with a swirl unit and straightener In Type B the distribution is obtained with grates Type A
Type B Velocity magnitude m/sec
Swirl Straightener
6.000 4.000 2.000 0.0000 -2.000 -4.000 -6.000 -8.000 -10.00 -12.00 -14.00 -16.00 -18.00 -20.00 -22.00
Grate
The FLSmidth Airtech concepts includes a swirl generator and straightener unit or a grate, depending of type, positioned in the GCT inlet. The concepts controls the flue gas distribution in the tower giving the following key advantages: y y y y
Product Description
y
Ensures hot flue gas at the tower wall, which prevents build-up of wet dust. Only downstream and hot flue gas around water injection nozzles. Low pressure drop across the tower. A good mix between water droplets and flue gas. Only lances of short length are needed.
Inlet transition Different types of inlet transition pieces are used, depending on the process involved and/or the local plant conditions. Type B-60
Type B-30
Type U-045
Type B-GV
Without guide vanes
Without guide vanes
With guide vanes
Swirl type A Grates type B
For GCT type A
For GCT type A and B
For GCT type A and B
For GCT type A and B
Layout examples
From cyclone
Cyclone tower
Product Description
Control Systems FLSmidth Airtech has developed the “Conditioning Tower Thermodynamic Regulation” (CTTR) unit for regulation of the water injection to the GCT. The control unit consists of two regulation systems: 1. The CTTR-system 2. The traditional Temperature Control System The CTTR-system is the primary control mode as it works faster and is more efficient than the Temperature Control System. (For special purpose the control unit can work with the traditional Temperature Control System only) Conditioning Tower Thermodynamic Regulation system (CTTR) The CTTR system controls the GCT by cascade/feed forward control, where the flow rate and temperature of the gases are measured before they enter the water evaporation zone of the GCT. This makes the regulation works faster and more efficiently than a traditional control system. The measurements are transmitted to a processor calculating the necessary water injection rate. The result is used to feed the quantity of water needed to condition the flue gases which will be present in the tower seconds later. The injection is finely adjusted by regulating in a small area according to the difference in the outlet temperature and the set point temperature. The CTTR system contains following functions: 1. Control and interlocking of the system 2. Monitoring of the measuring system 3. Calculation of the mass flow rate in the tower and the required water flow rate 4. Start/stop control of water pumps and valve rack 5. Selection of lances to be set in operation 6. Start/stop of lance groups in operation 7. Regulation of the outlet temperature 8. Handling of failures and warnings 9. Configuration of the measuring system 10. Configuration of the lance system 11. Configuration of the pump Configuration and adjustment of the system is performed on an operator panel (HMI). A philosophy of the GCT control is maximum fail-safe state, which is implemented as follows:
Product Description
Temp inlet Flow inlet Lance Thermodynamic Regulator Flow meter
Water Temp outlet
To increase safety and accuracy, the measuring transducers are double when possible. This is applied for the gas inlet and outlet temperature and pressure transmitters for air and water. In normal operation the average value of a pair is used, but if a pre-set difference between a pair is exceeded, only one is used and the system transmits a warning to the central control. The signal used for temperatures and water pressure is the highest value of default pair and for pressure transmitters the lowest value. 1.
2.
The system can work in 4 modes:
A “Cascade” or “Feed Forward”, which is the basic mode, requires that at least one of the measuring transducers of a pair is valid. However, in case both outlet temperatures are faulty, it continues to operate in this mode, but a warning is transmitted to the central control. “Temperature control”, a mode where the outlet temperature is required for the process. The system switches automatically down from “Cascade” to “Temperature control” in the following cases: B.
x x x
Both inlet temperatures are faulty. The gas flow rate cannot be measured. The water flow rate cannot be measured.
When the cause for switching to “temperature control” is eliminated, the control automatically switches back to “Cascade”.
Product Description
Configuration example
Product Description
“Flow control”: where the water spray rate is constant according to a value set from the panel. In case both the temperature for inlet and outlet are faulty, the GCT stops automatically and the flow control is enabled by switching to local mode. C.
“Valve control”: which is a mode where the position of the water valve is constant according to a valve set from the panel. In case all temperature and water flow rate measuring devices are faulty, the GCT stops automatically, but when switching to local mode the valve control is enabled. D.
In principle there is a 5th mode, operating without the control unit, but starting a pump locally and controlling the water flow by the bypass valve. The two phase injection system also has a control loop for the air mixture ratio. In case both pressure transmitters for the air are faulty, the GCT will stop automatically. However, selecting a full open by-pass for the air valve the system can work in all modes. In CENTRAL or remote control, only the A and B modes are possible. When setting LOCAL all modes are available.
Temperature Control System The traditional thermal control system is of the feedback type, it measures the outlet temperature of the GCT, and if this temperature varies from the set point temperature, the water supply to the GCT is regulated.
Water spraying system The water used for conditioning the kiln gas is injected with single nozzle lances one meter below the conical diffuser. Arrangement examples A-A
A
A
D
Product Description
FLSmidth Airtech uses two different types of water spraying systems. One system is the “Back Flow System” where part of the water that enters the nozzle is injected into the GCT and the rest returns to the water tank. The other system is the “Two Phase Injection System” where water is atomised with compressed air resulting in smaller drops at a high water volume flow rate. Because of the smaller droplet size, the tower for a Two Phase System has the lowest evaporation height. Technically, the two phase system is always preferable because of less wear on the nozzles than with the Back Flow System and a better water atomisation.
Back Flow System The back flow nozzle is designed to have an adjustable supply of water injection. This makes it is possible to vary the water supply according to process operations by changing the return pressure and keeping the supply pressure almost constant. Water is taken from the client’s supply line to the water tank and lifted up to the injection level by a high-pressure pump. The tank is supplied with a float valve and a low-level switch, which stops the pump and prevents pump damage in case of supply water problems. An overflow pipe and a high level switch gives an alarm in case of float valve malfunction. The pump pressure is approximately 40 bar g. It is supplied by one of two highpressure pumps mounted on a solid frame in parallel. The sealing between the shaft and the pump house can be either solid graphite seal or a flexible packing ring. Pressure transducer Manometer Flow meter Ring line
Non-return valve Strainer Stop valve P
Pump Duplex filter with pressure switch Pneumatic actuator
Conditioning Tower P
Water tank Water supply
Pneumatic valve
Dry flow feedback Overflow feedback
Thermocouple Gas flow meter Inlet water Back flow water Flue gas
Before the water reaches the lances, it passes through a duplex filter. The duplex filter contains two filter elements, one active and one spare. When the active filter is partially blocked, a valve is turned, isolating the contaminated filter and opening the parallel filter.
Product Description
Each lance is coupled to two ring pipes with flexible hoses. One ring pipe contains the supply water and the other the return water. The pressure of the return water differs between 0-18 bar g, as it passes the regulating valve and enters the water tank. The injected water rate is controlled via the return flow pressure by means of a pneumatically operated valve fitted to the return pipe. If the control valve is closed, all water from the water tank will be injected and if it is fully open, a minimum of water will be injected. Supply and return pressures are measured by pressure transducers giving electrical signals to the automatic control. For reading the supply and return pressure, two Bourdon manometers are fitted to the ring pipes. Likewise, for reading the pump pressure, a Bourdon manometer is fitted to the common supply pipe. If the automatic control for some reason is out of order, there is a manually controllable by-pass valve parallel to the regulating valve. Flow rate meters can be fitted to the supply pipe and to the return pipe and the signals from these transducers are an important part of the thermodynamic control system. Nozzle and lance for the back flow system The lance consists of an inner tube (the return water tube) and an outer tube. The two conduits are connected to the nozzle in the spraying end and to two-threaded pipe stubs at the other end. Inlet water Back flow water
Nozzle Pneumatic actuator Non-return valve Valve Flexible rubber hose Strainer
The Lance has two ball valves, one for the supply line and one for the return line. Furthermore, a strainer is positioned in the supply line and a check valve in the return line.
Product Description
If the control system is of the thermodynamic type, an extra shut-off valves with a common actuator are fitted together with a solenoid valve for controlling the on/off position of the lances. In special cases cooling air or purge air can be fitted onto the lance arrangement. The nozzle consists of a swirl disc supplied with "tangential" holes, a nozzle cap with a centre injection hole and a centre pipe for the return flow. The water at the nozzle wall is directed towards the nozzle exit hole, and the water in the centre region is directed towards the return hole.
Lance Inlet water Back flow water Nozzle
Two Phase Injection System The two phase injection system mixes compressed air and water creating an injection of exceptionally small drops. By controlling the air and water pressures the injection rate varies. Water is taken from client’s supply line to the water tank and lifted up to the injection level by a medium pressure pump. The air from compressors passes through the pressure vessel and on to the lances. The water tank is supplied with a float valve and a low level switch, which stops the pump and prevents it from self destruction in case of supply water problems. An overflow pipe and a high level switch gives alarm in case of float valve malfunction. The pump pressure is approximately 16 bar g. The sealing between the shaft and the pump house might be either solid graphite seal or a flexible packing ring. Normally two pumps are in parallel, always with one as standby.
Product Description
Pressure transducer Manometer Flow meter Ring line
Non-return valve B P
B
Block valve Stop valve
P
Pneumatic valve Relief valve
P
Conditioning Tower
Pump Duplex filter with pressure switch
Air B
Pneumatic actuator Water tank Pressure vessel Water supply
Dry flow feedback Overflow feedback
Thermocouple Gas flow meter Water Air Flue gas
More compressors can be applied depending on total air mass flow rate and demands for redundancy with one spare compressor. The pressures are 7,5 bar g (50 Hz) or 7,0 bar g (60 Hz). Before the water reaches the lances it passes through a duplex filter. The duplex filter contains two filter elements, one active and one spare. When the active filter, standard mesh size 200 µm, is partially blocked, a valve is turned, isolating the contaminated filter and opening the parallel filter. Each lance is coupled to two ring pipes with flexible hoses. One ring pipe consists the supply water and the other the supply air. Two pneumatically activated control valves for water and compressed air regulate water and air flow rates according to the needs of the specific nozzle types. In case of defective control valves, manually bypass valves can be utilised. Air and water pressures are measured by pressure transducers giving electrical signals to the automatic control. For reading the water pressure, two Bourdon manometers are fitted to the ring pipes. Flow rate meters are fitted to the water supply pipe and the signals from this transducer is an important part of the thermodynamic control system. From the supply pipe a shunt pipe with a damped relief valve will lead the water back to the tank if the supply pressure exceeds a limiting pressure.
Product Description
Nozzle and lance description for the two phase system The typical lance consists of two concentric tubes for water and air. The two conduits are connected to the nozzle in the spraying end, and to two threaded pipe stubs in the other end.
Air Water
Nozzle Pneumatic actuator Valve Flexible rubber hose
The lances are supplied with two shutoff valves and, if thermodynamic control is used, two extra solenoid valves are fitted together with a solenoid valve for controlling the air supply. The nozzle consists of a fluid tip with a centre hole for the water and smaller holes around it for the air. The two fluids are mixed in an air cap and hit a stump, and the droplets are ejected through small holes into the gas stream.
Air Water Lance Fluid tip Cap not Air guide Air cap
Product Description
Mechanical description Apart from dead loads, i.e. tower weight, weight from dust in hopper, and moveable weights on stairs, ladders and platforms, the tower is constructed to withstand wind loads and loads from earthquakes. This construction is specific, i.e. made for each tower individually
Inlet unit
Conical diffuser unit
Cylindrical unit
Supporting unit
Reinforcement unit
Transition unit
Hopper unit
The tower is also designed to withstand normal and excessive temperatures and gauge pressures.
The geometry of the GCT is put together by following parts: - An inlet unit (with a swirl generator) - A conical diffuser - A cylindrical unit with a supporting unit - A transition unit - A bottom hopper with gas outlet - Dust transport Conical diffuser unit The conical diffuser unit has an angle of 150 from vertical.
Product Description
Cylindrical unit with supporting unit The main body of the GCT consists of a cylindrical unit with a supporting unit. The cylindrical unit gives the tower its required volume for conditioning the flue gas.
In this unit the injection ports for the water injection are installed and one or more inspection doors.
Transition unit The transition connects the cylindrical unit with the bottom hopper and changes the cross-section from circular to rectangular. Bottom hopper with gas outlet The bottom hopper is of the longitudinal type and has a gas outlet from the side and dust transport in the bottom.
Dust transport The dust separated from the flue gas is removed from the hopper by a drag chain or a screw conveyor. The dust is normally discharged from the hopper by a standard air sluice, a motor driven double flap valve or a pneumatically activated slide gate. Insulation The tower is insulated in order to avoid corrosion and in order to avoid the possibility of too high temperature on the outside (safety). The hopper is also insulated in order to prevent dust from building up due to moisture.
Supports Pendular Support The pendular support is a combination of vertical columns and cross diagonals, both made of square tube profiles that are welded together during erection. The heat expansion of the GCT during operation is absorbed by the angular movement in relation to the points of support on the foundation. Direction of motion
Tower Spherical top
Guide ring
Guide ring
Foundation bolt Spherical top
Product Description
Concrete
Rigid Steel Support An alternative support is the traditional rigid steel support. When using the rigid steel support system, the GCT is equipped with a slide bearing, so the heat expansion of the GCT can take place safely. Direction of motion
Guide block
Securing bolt
GCT flange
Steel support (Teflon covered steel plate) 4, 8 or 12 bearings
Concrete Support An other alternative is the concrete support, in this system the GCT is also equipped with a slide bearing, so the heat expansion of the GCT is conducted safely. Direction of motion
Guide block
Securing bolt
GCT flange
Securing/Anchor bolt (Teflon covered steel plate)
Product Description
4, 8 or 12 bearings
Dust removal All dust is collected in the hopper and discharged via screw conveyor or drag chain, air slide, rotary air lock, double flap gate, slide gate. The solution of type depends of the process or cust omer requirement
Screw conveyor
GCT hopper
Ball bearing Drive station Screw, D=500 mm
Air lock Ball bearing
Drag chain
Turning station
GCT hopper Drive station
Ball bearing
Turning roller
300 mm chain
Traction wheel
Product Description
Ball bearing
Access Facilities For operation and maintenance purposes, the GCT is provided with the necessary access facilities. A gangway is mounted all the way around the tower at the level of the lances for operation of lances and maintenance. Gangways are made of sectional steel and grating is equipped with railing made of tubes. If ladders and gangways are included in the supply from F.L.Smidth Airtech, they can be made according to any standard. If no standard is specified, they are made according to the German DIN or the F.L.Smidth Airtech standard. Tube 48.3 x 3.2 Tube 26.9 x 2.6 Grate 30 x 30 x 3
0 0 1
1500 5 2 ø
0 0 0 9 x a M
500
0 0 0 0 1 5 1
0 0 0 0 0 2 3 2 x n a i M M
1000
Dimensioned for loads: 2 Walks. Evenly distributed 3kN/m Walks. Single load 3 kN within 100x100 mm Railings. Horizontal 0.4 kN/m Standard. DIN
Product Description
FLSmidth Airtech supplies Air Pollution Control equipment: Electrostatic precipitators • FabriClean pulse-jet fabric filters • Gas conditioning towers • Desulphurization systems • COROMAX pulse systems • PIACS microprocessor controllers and other advanced electrical control systems • Dust transport and storage equipment • All kinds of auxiliary equipment like fans, flue gas ducts, cyclones etc. • We supply new equipment or upgrading of existing equipment – no matter whether the existing equipment is supplied by us or not.
Ramsingsvej 30 DK-2500 Valby Tel. +45 3618 2000 Fax. +45 3618 2030 E-mail: info@flsairtech.com www.flsairtech.com
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