KRUG Ltd. Developed Fault-Tolerant Furnace Emergency Shutdown System

Furnace emergency shutdown causes plenty of problems and unpredictable consequences: defective production, necessity of restart, possible loss of integrity of flange connections, gas contamination, fire. One of the worst situations is emergency shutdown of the furnace by a false signal from the sensor: “bounce”, wrong measurement, etc.

Systems of furnace security are improved, the number of blocking parameters is increasing, and probability of false emergency signal is increasing as well. Sometimes it is more difficult to secure the furnace protection system against false signals than to realize the security system itself. Microprocessor means of technological process control allow making the furnace security system more “intelligent” and reliable. Security algorithms got a possibility to apply more complicated methods of protection against false signals based on analysis of simultaneous behavior of several signals.

Subsystem of furnace Emergency Shutdown System (ESS) which would comply with all the requirements of the effective regulatory documents and decrease the amount of false shutdowns to the minimal degree was developed by KRUG Ltd. in the result of upgrading of the automatic process control system of the atmospheric oil distillation plant (Rosneft – Tuapsinsky NPZ).

Furnace characteristics: updraft furnace with four fire-chambers, with raw stock supplied by one pump, four main burners and four pilot burners, pilot burner installed in the main burner throat.

Furnace ESS parameters:
Cease of raw stock supply to any coil of the furnace.
Excess of maximum permissible temperature of raw stock at any coil outlet.
Excess of maximum permissible temperature at the furnace bridgewall.
Decrease of furnace depression.
Decrease of fuel gas pressure at pilot burners.
Increase or decrease of fuel gas at main burners.
Operation of the flame extinguishing device.

To secure against “bounce” and interference, delays for emergency signal passing in the protection algorithm were introduced. If the signal is identified as a false one, then time delay for blocking actuation is set. In this case, the timer, light and audible alarms are activated. During this time period, the operating personnel make a decision and either activates the unblocking key, or blocking will actuate in two minutes.

Identification of a sensor signal as a false one is realized in the furnace security system:
ESS by raw stock rate to the furnace coils. In case of decrease of the rate of one of the flows, other flow rates are analyzed.
ESS by the raw stock temperature at the furnace coil outlet. In case of increase of raw stock temperature at the furnace outlet for one of the flows, behavior of this flow rate and temperature of other flows are analyzed.
ESS by the furnace gas temperature at the furnace bridgewall. In case of the furnace dam plate temperature increase, the total furnace load is analyzed by the rate.
ESS by the fuel gas pressure. In case of the fuel gas pressure drop, behavior of the rate of fuel gas to the furnace and condition of burner flame are analyzed.
ESS by depression in the furnace. In case of depression decrease in the furnace, the condition of the burner flame is analyzed.
ESS by flame extinguishing. Signal for the furnace blocking comes if two main burners and pilot burners in two adjacent throats went out.

The results of implementation of the furnace security system proved its efficiency. Improvement of the furnace ESS system intelligence resulted in the following:
Elimination of unpredictable operation of the security system.
Certain time available for the operating personnel to respond immediately to the situation.

Training of the operating personnel showed that the blocking delay in case of false signal is sufficient to ascertain its reason and exclude false emergency shutdown of the furnace.

All new technical solutions incorporated in the improved ADP system are realized in full compliance with the requirements of the teffective regulations and are included in the detailed engineering document which passed the industrial safety expert examination.

The fault-tolerant furnace ADP system was implemented on the basis of software-and-hardware complex PTK KRUG-2000 but the accepted technical solutions can be realized virtually in any modern control system.

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