SAFETY DEVICE FOR STEAM GENERATOR

SAFETY DEVICE FOR STEAM GENERATOR

The invention relates to steam generators.

More particularly, the invention relates to managing the risks inherent in the implementation of boilers.

More particularly, the invention relates to the functional reliability of the boiler.

The pressures and temperatures involved throughout operation of vapor generators involve risk to employees for using such machines.

In order to reduce these risks, to SIS safety instrumented systems are implemented.

In particular, securing assemblies are implemented and:

the level and quality of water in the heater of the steam generator;

the steam pressure;

the scrams.

The management of these sets of security is centralized in a switchgear cabinet.

The automaton combustion also comprises means for managing safety precautions related to the burner and the combustion.

A reduction level of risk for a given security function can be quantified by Lis safety integrity level (The Safety Biotic Integrity niveau in terminology is frequently), which extends on a scale of 1 to 4. The reliability of the safety instrumented system grows with LIS. The sIL takes into account the probability of occurrence and severity of risk and consequences thereof.

Figure 2 represents the correspondence table between safety integrity level SIL a reduction factor of SRR {Factor in infected patients terminology is frequently) equal to the inverse of the average probability of failure on demand of a PFD (Of marine Demand in organ failure terminology is frequently).

In accordance with IEC 61511, assigning a level Lis is effected using a graph risks, shown in Figure 3, based on four parameters:

gravity g of damage related to a risk;

the frequency f and/or exposure time;

the probability of occurrence of P_PLC of the hazardous event;

the probability P-avoidance_{the EV} said hazardous event.

Each of these parameters is quantified by a discrete scale:

The Gi: minor incident;

G₂ : severe injury leading to disability; death of a person;

G3: death of two persons;

G₄ : death of more than two persons;

F. I-: rare exposed at risk;

F₂ : permanent exposure at risk;

P_PLC I-: low probability of occurrence;

Pap2: average probability of occurrence;

Pap3: high probability of appearance;

ICP: event avoidable under certain conditions;

P_{the EV} 2: inevitable event.

The evaluation of four parameters grams, F., P._PLC and P_{the EV} , identifies the type of risk and, via the risk graph, the level of sIL required.

On the graph, the presence of a dash or a " has>>in a box presented when prescription for a particular security. The letter " b->>corresponds to a situation in which the use of instrumented systems is insufficient to ensure the safety of operators.

Safety integrity level Lis system depends on the level of integrity security component subsystems.

Conventionally, a safety instrumented system comprises a subsystem sensor (input interface), a logical subsystem subsystem and a actuator (output interface). The devices composing the subsystems can be arranged in series or in parallel.

To verify operability of the safety instrumented systems, placing periodic tests authenticating of the functioning ability is required. The frequency of these tests depends on the level Lis assigned to SIS.

Figure 4 represents the evolution of the probability of failure on demand of a PFD as a function of time for two sensors a and b associated with a level 2 Lis.

The sensor has, represented by a solid line curve, can be regarded as having a level 2 Lis during a unit of time, for example one year. Beyond, the average probability of failure PFD is too high. Should therefore ensure after one year in that the sensor is functioning properly. After verification, the sensor may be reused for one year without verification.

The sensor B, represented by a dotted curve, can be regarded as having a level 2 SILs for five units of time, such as five years. The operating state of the sensor B is thus verified that every five years.

The boilers currently used today are a security level 2 Lis. Such a level of security forces to many periodic testing to verify operability of the security systems. The embodiment of these tests involves the unavailability of the boiler test.

Currently, the elements used to perform the functions of safety require that regular tests, to periods of the order of one to six months after they also.

The invention concerns a safety system of a steam generator for providing a safety integrity level Lis equal to 3. Such an integrity level of security spaces the verification tests good operating security systems. In particular, with the device according to the invention, the security tests are to be performed only once a year.

The security device according to the invention is intended to be implemented on a steam generator, and comprises:

at least two pressure excess steam pressure;

at least two probes each having a water level safety integrity level Lis at least equal to 3;

at least two scrams-integrity security Lis at least equal to 3;

said safety device being characterized in that it further comprises:

an automatic safety connected to the at least two pressure switches, to the at least two probes and at least two emergency stops;

a relay assembly connected to the outputs of said automaton safety and suitable for acting on an automaton combustion, a food pump and regulating device of said steam generator to stop the latter in an emergency;

and that:

the at least two pressure switches each have an integrity level of safety at least equal to 2 Lis;

the pressure switches, the probes and emergency stops are independent of each other in their operation.

The invention also relates to a steam generator having an automaton combustion, a food pump, an automatic regulating device and a safety device according to the invention.

In one embodiment, the steam generator comprises:

a heater;

a burner combustion controlled by the switch;

a vessel feed water supplied to the heating body, the feed pump being disposed between said heater and said water tank.

In one embodiment, the automatic regulating device acts on the automatic combustion and on the feed pump.

In one embodiment, the steam generator is a boiler.

The invention will be better understood upon reading the description that follows and review of the accompanying drawings. These are just illustrative least and limiting of the invention.

Figure 1 represents a block diagram of a steam boiler equipped with security device according to the invention.

Figure 2 already cited represents a correspondence table between a safety integrity level SIL factor reduction SRR.

Figure 3 already cited represents the graph of risk for determining the level of integrity security Lis.

Figure 4 already cited represents the evolution of the probability of failure on demand of a PFD as a function of time for two sensors.

The invention relates to a safety device intended to be implemented on a steam boiler. The skilled person will include through-out the description that the invention is not limited to only boilers but can be implemented more generally on any type of steam generator.

With reference to Figure 1, the steam boiler 1 has:

a heater 10;

a burner 11 controlled by an automaton combustion 110;

a vessel 12 feed water supplied to the heating body 10 through a food pump 120;

an automatic regulating device 13 acting in particular on the automatic combustion 110 of the burner 11 and on the feed pump 120.

Of course, Figure 1 represents a steam boiler 1 in a simplified manner, and the boiler 1 includes other elements not shown, e.g. a natural gas feed, a vent, a chimney, conductivity probe, control valve, andc.

A heat produced by the burner 11 is transmitted to the food contained in the water heater body 10. Such heat exchange is for example performed via combustion of a fuel element, such as fuel oil or gas (not shown).

A portion of the heated water becomes steam thereafter can be exploited. The burner 11 is controlled by the state machine 110 combustion equipment sends a set power for managing the amount of steam produced.

The pressures and temperatures involved involve risk to employees for using such boilers.

With reference to Figure 1, a safety device according to the invention is implemented to ensure safety of personnel. The device according to the invention comprises:

two pressure switches 20 of excess steam pressure;

two probes 21 very low water level;

two scrams 22;

an automatic safety 23;

a relay assembly 24.

The pressure switches 40 of excess pressure steam can detect an abnormal rise of pressure within the boiler. The two pressure switches 40 are mounted on the boiler independently. These pressure switches each have a safety integrity level Lis equal to two, e.g. a pressure switch Company (registered trademark) Georgin's, and symbolized graphically by a double edge.

The probes 41 of very low water level control the minimum water level within the generator. Each of the probes used has an integrity level security Lis equal to three, symbolized graphically by a triple edge. It may be for example of probes of the company GESTRA (registered trademark).

The two scrams 42 are arranged on a respective side of the heating body 10 and to an electrical cabinet 14 and each have a safety integrity level three Lis, symbolized graphically by a triple edge. They can be selected for example in the range products (registered trademark) PILZ.

The pressure switches, water level probes and scrams form safety contacts connected to the automaton 23 security input via electrical connections 25. The automaton safety 23 has a security level of integrity Lis equal to four, symbolized graphically by a quad edge.

The set of relay 24 is connected to the outputs of the automaton of security through output line connections 26, and acts directly on the automatic combustion 110 associated with the burner 11, on the feed pump 120 water supply food, and on the automatic regulating device 13 for stopping the boiler in an emergency. Advantageously, the number of elements constituting the assembly of relaying is limited with respect to sets of relaying currently existing in order to reduce the probability of failure of a member of the relay and thereby the boiler.

The terminology electrical connection input/output electrical connection is selected with reference to the set safety automaton relay assembly 23 and 24, the information transmitted by the safety contacts are provided as inputs of the assembly, and the orders sent to the automaton combustion 110, 120 and food to the pump control circuit providing at outputs of said assembly. The electrical connections are symbolized in Figure 1 by dashed lines.

The security device according to the invention has a safety integrity level Lis equal to three. The characteristics for providing such security level are as follows:

lis safety integrity level safety contacts carried out, in particular, implementing security level of pressure switches Lis equal to two;

redundancy and independence of safety contacts used, in particular, the two pressure switches 20 are independent of each other, similarly the probes 21 and 22 emergency stops are members which are independent of each other;

The advantages of a boiler having a safety device according to the invention in comparison with a conventional boiler are as follows:

the material used has a security level increased and failure rate lower;

the security tests in real, mandatory to validate the proper operation of the safeties, is performing every year, due to the security level of integrity Lis reaches. The boilers prior requiring security tests spaced up to about six months, this advantage is particularly advantageous in that the boiler must be stopped during these tests, stopping production steps that require the use of the boiler, and therefore has a constraint for operators having economic implications. A boiler equipped with a safety device according to the invention is thus available 365 consecutive days.

Calculating the level of integrity security Lis three was made enabled by the organism notified APAVE.