CLIAMS:We Claim:

1. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants comprising

a plurality of impulse pipes in hood with means for transmission of pressure impulse involving a main pipeline ;
a cooperative pipeline with valve means to which an input of solenoid transmitter is connected for skirt pressure measuring;
a cooperative pipeline with valve means having a solenoid purging input operatively connected to nitrogen header with its outpur connected to said main pipeline for passing nitrogen for purging;
PLC with logic controller for desired sequential operation of valves and transmitters for desired purging.

2. An auto purging system as claimed in claim 1 comprising

a plurality of impulse pipes positioned at the peripheral of lower portion of hood in circular circumference equally spaced; said impulse pipes joined through a common header so that all impulse pipes are parallel to each other and pressure measured is summed average of all impulses;
said common header adapted to transmit pressure impulse to a single impulse pipe connected through a hose;
two tapings T1 and T2 of impulse taken from said main single impulse pipe line, which are connected to individual transmitters wherein
c) in said taping line T1 a first solenoid valve for pressure transmit is fitted, said solenoid valve output is bifurcated for two skirt pressure measuring pressure transmitters;
d) in taping line T2 a second solenoid valve for purging is fitted, said Solenoid purging input is connected to nitrogen header with audco valve in line and output of solenoid purging is connected to said main impulse line for passing nitrogen for desired purging.

PLC with logic programme for desired sequential operation of valves and transmitters for desired purging.
electrical power connections to both said solenoid valves operatively from said PLC in control room.
HMI screen for the operator to select the appropriate transmitter reading for control of skirt pressure based on readings from the two pressure transmitters displayed in control room.
3. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants as claimed in claim 1 wherein said impulse pipes comprising 8 impulse pipes positioned at the peripheral of lower portion of hood in circular circumference 45 deg apart to each other.
4. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants as claimed in anyone of claims 1 or 2 wherein the range of the skirt pressure parameter measured by pressure transmitters is - 5 mmwc to +5 mmwc for carrying out suppressed combustion of furnace gases.
5. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants as claimed in anyone of claims 1 to 3 adapted for purging of impulse pipes automatically after each blow and slag splashing for 15 minutes using nitrogen at 10 kg/cm2 pressure.
6. A method for of carrying out auto purging of skirt pressure impulse lines using the system as claimed in claims 1 to 5 comprising

measuring skit pressure involving solenoid transmitter and differential pressure inputs;
involving a solenoid purging input operatively connected to a nitrogen header with its output connected to said main skirt impulse pipeline for passing nitrogen for purging;
involving a PLC with logic controller for desired sequential operation of valves and transmitters for desired purging.

7. A method as claimed in claims 6 comprising
(i) under normal condition with no blow and slag splashing opening solenoid transmitter and measuring skirt pressure involving two transmitters and closing solenoid purging such that no nitrogen is passed;
(ii) following same operation under (i) above during Blow and slag splashing-;
(iii) Just after lifting of lance after finishing blow or slag splashing closing solenoid transmitter immediately and opening soleniod purging after desired duration , thus allowing nitrogen to pass through the impulse pipes and clean the pipes and their mouths from slag and dust by purging with nitrogen for sufficient time during which time the system does not get the skirt pressure reading as solenoid transmitter remains closed.
(iv) After sufficient period of lance lifting, closing solenoid purging to thereby stop nitrogen purging and opening solenoid transmitter for desired time thereafter to get back the readings of skirt pressure and thus bringing the system back to the stage of step (i) and completing the cycle .

(v) A method as claimed in claim 7, wherein the time lag of 5 sec between opening and closing of solenoid is provided to avoid damage of pressure transmitters as 10 kg/cm2 pressure of nitrogen may damage these low range transmitters.

Dated this the 1st day of April, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

,TagSPECI:FIELD OF THE INVENTION

The present invention relates to auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants. More particularly, the present invention is directed to providing a system for controlled auto purging of the tapping points of impulse pipes for measuring Skirt Pressure, positioned at the peripheral of lower portion of hood in circular circumference 45 deg apart to each other involving high pressure nitrogen back purging after each heat making and slag wash in converter, thus not allowing dust to be settled at the mouth of the impulse lines preventing it from choking. The new system is not only more efficient and clean, but has forever replaced manual purging with a more ergonomic and speedy alternative. The system employs PLC based control of auto purging of impulse lines favouring correct measurement of Skirt pressure for controlling damper movement which in turn controls the draught in Gas duct of Gas Cleaning Plant required for suppressed combustion in LD Convertor Shop. Also the system ensures the skirt pressure parameter to be available throughout the convertor campaign which in turn ensures the damper operation in auto mode always.

BACKGROUND OF THE INVENTION
i) Conventional Suppressed Combustion System in LD convertors of Steel Plants

Gas cleaning plants of LD convertors are provided with IRSID/CAFL method of suppressed combustion system. The basic feature of this process is that the suppressed combustion of furnace gas is achieved without the need of an inert gas supply from external source. This is achieved by first burning the convertor gases under combustion open conditions with air and then reducing the induced air by means of a draught regulator until suppressed combustion is achieved.

With the suppressed combustion system the most important operation during a blow is the ignition of the furnace gas before lowering the skirt. Once the furnace gases have been ignited, the formation of inert gas barrier at the change over point from full combustion to suppressed combustion and again back to full combustion is carried out by physical phenomena which cannot be prevented.

When suppressed combustion is going on, the entry of atmospheric air is prevented through hood pressure control. A positive pressure is maintained at the neck of the convertor and at the same time the total gas cleaning system has been made gas tight. This has been done to avoid any entry of atmospheric air inside the system. The oxygen blowing is automatically stopped if the oxygen analyzer read oxygen above 2% and then complete system is evacuated fully by taking maximum flow through the system.

The skirt is positioned between the top of the vessel and the lower edge of the hood. At the beginning of the blow, skirt is held in its raised position and the complete combustion of the gas is allowed to take place.

During the complete combustion phase the draught regulator is held in a pre-set position which allows combustion to take place with upto 200% excess air.

After beginning of the blow once oxygen is on and the ignition of convertor gases has been observed, the skirt must be lowered. When the skirt reaches its lower position, the limit switches changes, the draught control from a pre-set full combustion to a modulating system in which the waste gases are evacuated in exact proportion to their evolution. During this change over the draught regulator closes on its own, taking signals from hood pressure control and the system passes from full combustion with O2 rich waste gas. All the air drawn in this is consumed in burning evolved carbon monoxide and carbon di-oxide and the resultant waste gas is a mixture of CO2 and N2 thus forming an inert gas barrier between O2 rich gases and CO rich gases.

At the end of the blow, the skirt is raised and draught regulator adjusts to its open position and once again the inert slug is automatically produced isolating CO rich and O2 rich gases.

ii) Skirt Pressure Measurement:
Skirt pressure is measured through 8 impulse pipes positioned at the peripheral of lower portion of hood in circular circumference 45 deg apart to each other.

Now these 8 impulse pipes are joined through a common header. This arrangement makes all eight impulse pipes parallel to each other and pressure measured is summed average of all impulses.

The common header now transmits pressure impulse through a single impulse pipe. From this single impulse pipe two tapings are taken for two transmitters.

Skirt pressure is very vital parameter for suppressed combustion. Whole process of suppressed combustion depends on this parameter. So, for redundancy purpose there are two skirt pressure measuring transmitters are used. Readings from these two transmitters are displayed in controller room. Which of the reading is used for control of skirt pressure is software selectable and operator selects the appropriate transmitter reading on HMI screen.
Range of the skirt pressure parameter is -5 mmwc to +5 mmwc.
iii) Control Section For Skirt Pressure
It is known that for suppressed combustion of vessel, the atmospheric air flow to the convertor mouth and GCP has to be cut. To achieve this during blow after skirt is lowered the skirt pressure should be slightly higher than the atmospheric pressure. This restricts the flow of atmospheric air to the GCP system as the natural draught is from high pressure to low pressure.

For creating the pressure higher than the atmospheric pressure under the skirt and at the mouth of the convertor, a butterfly control valve is used at the attack level. This in common terminology called the damper. Damper restricts or damps the flow of gases through stack that is sucked by ID fan for creating pressure and vice-versa. Damper movement is pneumatically controlled by PI (proportional and integral controller) controller in PLC.

Now during blow the controller works in auto mode. GCP operator chooses the set point slightly above the atmospheric pressure in the range of +0.9 to +1.20 mmwc.
The control methodology is as follows:
a) When the skirt pressure is less than the set point, damper closes to restrict the gas flow which in turn increases the volume of gas at skirt and convertor mouth leading to create more pressure and achieve the set point.
b) When the skirt pressure is more than the set point, damper opens to facilitate the gas flow which in turn decreases the volume of gas at skirt and convertor mouth leading to create less pressure and achieve the set point

iv) Problem Of Skirt Pressure Measurement:
As already stated that the skirt pressure is measured by 8 impulse pipes. These impulse pipes are at the mouth of the hood and under the skirt. The opening mouth of these impulse pipes is jammed and pipes are choked by the slag and dust which is evolved during blow and slag splashing. After choking of impulse tubes the skirt pressure impulse cannot be transferred to the pressure transmitters. So, the pressure transmitters’ gives erroneous reading which in turn effects the damper movement through control loop.

To clean the mouth and impulse pipe nitrogen is purged to these eight impulse pipe so that slag and dust is cleaned. If any of the impulse pipes is jammed or choked it cannot be repaired during the operation of convertor. It is changed only in campaign repair of convertor.

v) Remedy For Choking And Jamming-

The remedy for the impulse pipe jamming and choking is to purge back the impulse pipes time to time with compressed air or nitrogen.

Manual Purging Scheme in the existing practice involves transferring the pressure impulse from header to common transmitter pipe with a hose. One end of hose is connected to common header and other to the quick coupling. For manual purging the technician disconnects quick coupling from transmitter side and connects it to compressed airline. Then he has to wait for half an hour at 23 meters after that he reverses the process.

vi) Drawback of manual purging and source for innovation
a) Only purged once in 24 hours. This gives the time to slag and dust to settle down and choke the impulse pipe. Practically purging should be done after each blow and slag splashing.
b) Requires manpower to be engaged at least half an hour per convertor.
c) Chances of leakage from hose and quick coupling.

In each campaign it is found that at least 6 of impulse pipe choked and others are partially choked. Changing 6 impulse pipes in each campaign repair is a huge task that requires manpower and time. This necessitated exploring the solution to this recurring problem.

There has been therefore a continuing need in the art to developing a system for implementing an auto purging scheme in which the purging of impulse pipes can be done automatically at desired intervals after each blow and slag splashing for desired duration at desired pressure using suitable purging medium to favour reduction in manpower involvement, reduction in plant downtime and ensure reliable measurement of skirt pressure without any choking/jamming problem of the impulse pipe lines.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to providing a controlled auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants involving controlled auto purging of the tapping points of impulse pipes for measuring Skirt Pressure, positioned at the peripheral of lower portion of hood using high pressure nitrogen back purging after each heat making and slag wash in converter, thus not avoiding choking/jamming of impulse lines and ensuring reliable measurement of skirt pressure.

A further object of the present invention is directed to a controlled auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants wherein Skirt pressure can be maintained throughout convertor campaign as there is no choking in the pipes.

A still further object of the present invention is directed to a controlled auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants wherein by passing nitrogen after blow and slag wash, the impulse pipes are cooled down, thus no broken and damaged pipes occurs during campaign.

Yet another object of the present invention is directed to a controlled auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants wherein manual purging of skirt pressure lines is avoided thus saving substantial manpower.

A still further object of the present invention is directed to a controlled auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants wherein consistent GCP-operation can be achieved by reliable working of skirt pressure parameter.

A still further object of the present invention is directed to a controlled auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants wherein wastage of compressed air can be stopped.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide an auto purging system for skirt pressure impulse lines in LD convertors of steel plants comprising

a plurality of impulse pipes in hood with means for transmission of pressure impulse involving a main pipeline ;
a cooperative pipeline with valve means to which an input of solenoid transmitter is connected for skirt pressure measuring;
a cooperative pipeline with valve means having a solenoid purging input operatively connected to nitrogen header with its output connected to said main pipeline for passing nitrogen for purging;
PLC with logic controller for desired sequential operation of valves and transmitters for desired purging.

A further aspect of the present invention is directed to said auto purging system comprising
a plurality of impulse pipes positioned at the peripheral of lower portion of hood in circular circumference equally spaced; said impulse pipes joined through a common header so that all impulse pipes are parallel to each other and pressure measured is summed average of all impulses;
said common header adapted to transmit pressure impulse to a single impulse pipe connected through a hose;
two tapings T1 and T2 of impulse taken from said main single impulse pipe line, which are connected to individual transmitters wherein
a) in said taping line T1, a first solenoid valve for pressure transmit is fitted, said solenoid valve output is bifurcated for two skirt pressure measuring pressure transmitters;
b) in taping line T2, a second solenoid valve for purging is fitted, said Solenoid purging input is connected to nitrogen header with audco valve in line and output of solenoid purging is connected to said main impulse line for passing nitrogen for desired purging.

PLC with logic programme for desired sequential operation of valves and transmitters for desired purging.
electrical power connections to both said solenoid valves operatively from said PLC in control room.
HMI screen for the operator to select the appropriate transmitter reading for control of skirt pressure based on readings from the two pressure transmitters displayed in control room.
A still further aspect of the present invention is directed to said auto purging system for skirt pressure impulse lines in LD convertors of steel plants wherein said impulse pipes comprising 8 impulse pipes positioned at the peripheral of lower portion of hood in circular circumference 45 deg apart to each other.
Yet another aspect of the present invention is directed to said auto purging system for skirt pressure impulse lines in LD convertors of steel plants wherein the range of the skirt pressure parameter measured by pressure transmitters is - 5 mmwc to +5 mmwc for carrying out suppressed combustion of furnace gases.
A further aspect of the present invention is directed to said auto purging system for skirt pressure impulse lines in LD convertors of steel plants adapted for purging of impulse pipes automatically after each blow and slag splashing for 15 minutes using nitrogen at 10 kg/cm2 pressure.
A still further aspect of the present invention is directed to a method of carrying out said auto purging of skirt pressure impulse lines using the system as described above, comprising

measuring skit pressure involving solenoid transmitter and differential pressure inputs;
involving a solenoid purging input operatively connected to a nitrogen header with its output connected to said main skirt impulse pipeline for passing nitrogen for purging;
involving a PLC with logic controller for desired sequential operation of valves and transmitters for desired purging.

A still further aspect of the present invention is directed to said method comprising
(i) under normal condition with no blow and slag splashing opening solenoid transmitter and measuring skirt pressure involving two transmitters and closing solenoid purging such that no nitrogen is passed;
(ii) following same operation under (i) above during Blow and slag splashing;
(iii) Just after lifting of lance after finishing blow or slag splashing, closing solenoid transmitter immediately and opening soleniod purging after desired duration, thus allowing nitrogen to pass through the impulse pipes and clean the pipes and their mouths from slag and dust by purging with nitrogen for sufficient time during which time the system does not get the skirt pressure reading as solenoid transmitter remains closed.
(iv) After sufficient period of lance lifting, closing solenoid purging to thereby stop nitrogen purging and opening solenoid transmitter for desired time thereafter to get back the readings of skirt pressure and thus bringing the system back to the stage of step (i) and completing the cycle .

Yet another aspect of the present invention is directed to said method, wherein the time lag of 5 sec between opening and closing of solenoid is provided to avoid damage of pressure transmitters as 10 kg/cm2 pressure of nitrogen may damage these low range transmitters.
The objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DECSRIPTION OF THE ACCOMPANYING FIGURES

Figure 1: is the schematic arrangement of auto purging system for the purging of impulse pipes according to the present invention showing the different components in the system for carrying out purging for 15 minutes automatically after each blow and slag splashing with nitrogen at 10 kg/cm2 pressure.

Figure 2: shows schematically the control loop for automatized skirt pressure control according to the present invention.

Figure 3: is the schematic view of the capacitive pressure sensor used in the system.

Figure 4: show the schematic sectional views of the solenoid valves used in the system wherein (a) shows the solenoid at rest, valve closed condition and (b) solenoid active, valve open condition.

DETAILED DESCRIPTION OF THE INVENTION WITH REFRENCE TO THE ACCOMPANYING FIGURES

The present invention is directed to providing a controlled auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants involving controlled auto purging of the tapping points of impulse pipes for accurately measuring Skirt Pressure required for implementing suppressed combustion by Gas cleaning plants of LD convertors.

The auto purging system according to the present invention is implemented by modification in
A) Mechanical Modification
B) Electrical Scheme
C) PLC logic

To implement the above system following modifications to the design configuration have been incorporated:
A)- Mechanical modification
As seen from conventional system that there are two tapings T1 and T2 of impulse from main line and they are connected to individual transmitters.
In new scheme the modification are done as follows
a) In line T1 solenoid transmitter is fitted.
b) Solenoid transmitter output is bifurcated for both transmitter
c) In line T2 solenoid purging is fitted.
d) Solenoid purging input is connected to nitrogen header with audco valve in line
e) Output of solenoid purging is connected to main line L for passing nitrogen for purging.
B) – Electrical scheme
Solenoids used in the scheme are of 220V AC each. Therefore the scheme requires 4 core cable to carry power to both of them from PLC in control room to 23 mtrs level.
Available four spare cables in a Junction box near the system is used for the power connection.

C)- Instrumentation logic-

The logic program in GE-FANUC PLC is indigenously developed . This program works according to the logic of operation explained under the section working of the system as follows.

In auto purging scheme the purging of impulse pipes is done automatically after each blow and slag splashing for 15 minutes with nitrogen at 10 kg/cm2 pressure.

Accompanying Figure 1 shows the schematic arrangement of auto purging system for the purging of impulse pipes according to the present invention showing the different components in the system for carrying out purging for 15 minutes automatically after each blow and slag splashing with nitrogen at 10 kg/cm2 pressure.

Accompanying Figure 2 shows schematically the control loop for automatized skirt pressure control according to the present invention.

Working of the auto purging system
The working of the system is explained in following conditions
1)- Normal condition – (No blow and slag splashing )
In this condition solenoid Transmitter is opened and skirt pressure is measured by both transmitters. Solenoid Purging is closed, so no nitrogen is passed.

2)- During Blow and slag splashing-Same as in step 1
3)- Just after lance lifted – (i.e blow or slag splashing is finished)
At this moment of time Solenoid transmitter gets closed immediately and Soleniod Purging gets opened after 5 seconds. This allows nitrogen to pass through the impulse pipes and clean the pipes and their mouths from slag and dust. The nitrogen purging is done through 15 mins. As solenoid transmitter is closed the system doesn’t get the skirt pressure reading.

4) After 15 min of lance lifting
Now solenoid purging closes to stop nitrogen purging and solenoid transmitter opens after 5 seconds to get back the readings of skirt pressure. The time lag between opening and closing of solenoid is provided to avoid damage of pressure transmitters as 10 kg/cm2 pressure of nitrogen damages these low range transmitters.

System is back now at the stage of step-1, so cycle is completed.

The instruments used in the auto purging system are having the features as stated below:
A) Pressure transmitter this includes:
Capacitive Pressure Sensors:
Capacitive pressure sensors use a thin diaphragm, usually metal or metal-coated quartz, as one plate of a capacitor. The diaphragm is exposed to the process pressure on one side and to a reference pressure on the other. Changes in pressure cause it to deflect and change the capacitance. The change may or may not be linear with pressure and is typically a few percent of the total capacitance. The capacitance can be monitored by using it to control the frequency of an oscillator or to vary the coupling of an AC signal. It is good practice to keep the signal-conditioning electronics close to the sensor in order to mitigate the adverse effects of stray capacitance. Accompanying Figure 3 shows the schematic view of the capacitive pressure sensor used in the system.

Pressure Transmitter:
The sensor output signal needed to be amplified to transmit the sensor signal over large distances around the plant without attenuation. Many types of amplified signals have been developed over the years as electronics have advanced and power considerations have changed but the 2 wire 4-20mA current loop output has long been accepted worldwide as the main method for transmitting pressure sensor signals over long distances and is still the most requested output signal particularly in the process control industry. So a pressure transmitter is simply a pressure sensor with some extra electronics to transmit a 4 to 20 mA output signal

B) Solenoid Valve:

A solenoid valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports. Multiple solenoid valves can be placed together on a manifold.

Solenoid valves are the most frequently used control elements in fluidics. Their tasks are to shut off, release, dose, distribute or mix fluids. They are found in many application areas. Solenoids offer fast and safe switching, high reliability, long service life, good medium compatibility of the materials used, low control power and compact design.

Besides the plunger-type actuator which is used most frequently, pivoted-armature actuators and rocker actuators are also used.

Accompanying Figure 4 show the schematic sectional views of the solenoid valves used in the system wherein (a) shows the solenoid at rest, valve closed condition and (b) solenoid active, valve open condition.

A solenoid valve has two main parts: the solenoid and the valve. The solenoid converts electrical energy into mechanical energy which, in turn, opens or closes the valve mechanically. A direct acting valve has only a small flow circuit, shown within section E of this diagram (this section is mentioned below as a pilot valve). This diaphragm piloted valve multiplies this small flow by using it to control the flow through a much larger orifice.
Solenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control. A spring may be used to hold the valve opened or closed while the valve is not activated.

The diagram shows the design of a basic valve. At the top figure 4(a) is the valve in its closed state. The water under pressure enters at A. B is an elastic diaphragm and above it is a weak spring pushing it down. The function of this spring is irrelevant for now as the valve would stay closed even without it. The diaphragm has a pinhole through its center which allows a very small amount of water to flow through it. This water fills the cavity C on the other side of the diaphragm so that pressure is equal on both sides of the diaphragm, however the compressed spring supplies a net downward force. The spring is weak and is only able to close the inlet because water pressure is equalised on both sides of the diaphragm.

In the previous configuration the small conduit D was blocked by a pin which is the armature of the solenoid E and which is pushed down by a spring. If the solenoid is activated by drawing the pin upwards via magnetic force from the solenoid current as in figure 4(b), the water in chamber C will flow through this conduit D to the output side of the valve. The pressure in chamber C will drop and the incoming pressure will lift the diaphragm thus opening the main valve. Water now flows directly from A to F.

When the solenoid is again deactivated and the conduit D is closed again, the spring needs very little force to push the diaphragm down again and the main valve closes. In practice there is often no separate spring, the elastomer diaphragm is moulded so that it functions as its own spring, preferring to be in the closed shape.

From this explanation it can be seen that this type of valve relies on a differential of pressure between input and output as the pressure at the input must always be greater than the pressure at the output for it to work. Should the pressure at the output, for any reason, rise above that of the input then the valve would open regardless of the state of the solenoid and pilot valve.

It is thus possible by way of the present invention to providing an auto purging system for skirt pressure impulse lines in LD convertors of steel plants to ensure correct and consistent measurement of skirt pressure to implement suppressed combustion of converter gases in a reliable manner avoiding choking/jamming of the impulse lines. The auto purging system according to the present invention is capable to provide following advantages:
Technical benefits
(i) Skirt pressure can be maintained throughout convertor campaign as there is no choking in the pipes
ii) By passing nitrogen after blow and slag wash cools down the impulse pipes , so no broken and damaged pipes during campaign
Man power saving
(iii) Routine job of purging of skirt pressure lines in general shift is now abolished. So, saving in manpower.
Quality improvement
(iv) Skirt pressure can be maintained throughout convertor campaign.
Customer Care / Delight
(v) Very less complain of skirt pressure parameter not working by GCP-operation of SMS 2.
Energy Saving
(vi) Wastage of compressed air stopped.
Cost Control & Cost Optimization
(vii) Manpower saved – 2 manpower one hour per day –routine job avoided.

We Claim:

1. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants comprising

a plurality of impulse pipes in hood with means for transmission of pressure impulse involving a main pipeline ;
a cooperative pipeline with valve means to which an input of solenoid transmitter is connected for skirt pressure measuring;
a cooperative pipeline with valve means having a solenoid purging input operatively connected to nitrogen header with its outpur connected to said main pipeline for passing nitrogen for purging;
PLC with logic controller for desired sequential operation of valves and transmitters for desired purging.

2. An auto purging system as claimed in claim 1 comprising

a plurality of impulse pipes positioned at the peripheral of lower portion of hood in circular circumference equally spaced; said impulse pipes joined through a common header so that all impulse pipes are parallel to each other and pressure measured is summed average of all impulses;
said common header adapted to transmit pressure impulse to a single impulse pipe connected through a hose;
two tapings T1 and T2 of impulse taken from said main single impulse pipe line, which are connected to individual transmitters wherein
c) in said taping line T1 a first solenoid valve for pressure transmit is fitted, said solenoid valve output is bifurcated for two skirt pressure measuring pressure transmitters;
d) in taping line T2 a second solenoid valve for purging is fitted, said Solenoid purging input is connected to nitrogen header with audco valve in line and output of solenoid purging is connected to said main impulse line for passing nitrogen for desired purging.

PLC with logic programme for desired sequential operation of valves and transmitters for desired purging.
electrical power connections to both said solenoid valves operatively from said PLC in control room.
HMI screen for the operator to select the appropriate transmitter reading for control of skirt pressure based on readings from the two pressure transmitters displayed in control room.
3. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants as claimed in claim 1 wherein said impulse pipes comprising 8 impulse pipes positioned at the peripheral of lower portion of hood in circular circumference 45 deg apart to each other.
4. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants as claimed in anyone of claims 1 or 2 wherein the range of the skirt pressure parameter measured by pressure transmitters is - 5 mmwc to +5 mmwc for carrying out suppressed combustion of furnace gases.
5. An auto purging system for skirt pressure impulse lines in LD convertors of steel plants as claimed in anyone of claims 1 to 3 adapted for purging of impulse pipes automatically after each blow and slag splashing for 15 minutes using nitrogen at 10 kg/cm2 pressure.
6. A method for of carrying out auto purging of skirt pressure impulse lines using the system as claimed in claims 1 to 5 comprising

measuring skit pressure involving solenoid transmitter and differential pressure inputs;
involving a solenoid purging input operatively connected to a nitrogen header with its output connected to said main skirt impulse pipeline for passing nitrogen for purging;
involving a PLC with logic controller for desired sequential operation of valves and transmitters for desired purging.

7. A method as claimed in claims 6 comprising
(i) under normal condition with no blow and slag splashing opening solenoid transmitter and measuring skirt pressure involving two transmitters and closing solenoid purging such that no nitrogen is passed;
(ii) following same operation under (i) above during Blow and slag splashing-;
(iii) Just after lifting of lance after finishing blow or slag splashing closing solenoid transmitter immediately and opening soleniod purging after desired duration , thus allowing nitrogen to pass through the impulse pipes and clean the pipes and their mouths from slag and dust by purging with nitrogen for sufficient time during which time the system does not get the skirt pressure reading as solenoid transmitter remains closed.
(iv) After sufficient period of lance lifting, closing solenoid purging to thereby stop nitrogen purging and opening solenoid transmitter for desired time thereafter to get back the readings of skirt pressure and thus bringing the system back to the stage of step (i) and completing the cycle .

(v) A method as claimed in claim 7, wherein the time lag of 5 sec between opening and closing of solenoid is provided to avoid damage of pressure transmitters as 10 kg/cm2 pressure of nitrogen may damage these low range transmitters.

Dated this the 1st day of April, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TITLE: AN AUTO PURGING SYSTEM FOR SKIRT PRESSURE IMPULSE LINES IN LD CONVERTORS OF STEEL PLANTS.

The present invention relates to auto purging system for skirt pressure impulse lines in LD Convertors of Steel Plants for controlled auto purging of the tapping points of impulse pipes for measuring Skirt Pressure, positioned at the peripheral of lower portion of hood in circular circumference 45 deg apart to each other involving high pressure nitrogen back purging automatically after each blow and slag splashing, thus not allowing dust to be settled at the mouth of the impulse lines preventing it from choking. The new system is not only more efficient and clean, but has replaced manual purging as a reliable, more ergonomic and speedy alternative. The system employs PLC based control of auto purging of impulse lines favouring correct measurement of Skirt pressure for controlling damper movement which in turn controls the draught in Gas duct of Gas Cleaning Plant required for suppressed combustion in LD Convertor Shop.
(Figure 1)