JKP Subotička toplana Control system of boiler 35MW in Subotica heating plant
The consortium of companies: „Remming” (mechanical works), and „Mikro Kontrol“ (electrical and control system works), within reconstruction of boiler room in Subotica heating plant performed adaptation of boiler room, production and installation of a RHW 35 hot water boiler with capacity of 35MW, with pipelines and implementation of control system.

Within the project, existing boiler room is adapted and delivery scope includes boiler, Eco, fresh air heater device (Luvo), gas and oil burning device, pipes for fresh air and exhaust gases; along with electrical installations of boiler system, the requests were reconstruction of transformer station, designing, mounting and wiring of general electrical installations (lighting, electrical sockets), lightning protection installations and anti-fire installations.

Boiler comprises one combined burner designed for natural gas and oil combustion; Boiler management system (BMS) is based on fail-safe control system S7-315F CPU, and designed according to international standards which regulate safety systems in process industry (IEC 61508 and IEC 61511). The BMS has to control burner firing, to regulate the load (by changing gas / oil – air ratio), to monitor critical process parameters; it communicates with supervising boiler control system (BCS) through ProfiBUS DP, and exchanges all the necessary information (start conditions, interlocks, load reference value, alarms).

The hot water boiler 35MW is designed, manufactured, installed and commissioned according to directives which regulate pressure water-type boiler installations (ISO 12952); technical requests by tender documentation that had to be fulfilled were:

1. gas emissions limit values (according to relevant directives in Republic of Serbia ):
SO2: 35mg/m3 (gas) and 850 mg/m3 (oil)
NOx: 150 mg/m3 (gas) and 450 mg/m3 (oil)
CO: 100 mg/m3 (gas) and 175 mg/m3 (oil)
dust: 5 mg/m3 (gas) and 50 mg/m3 (oil)
2. boiler capacity:
nominal output: 35 MW
minimal output: 4,4 MW
3. Efficiency at 100% output: 97% (gas) and 90% (oil)
4. boiler process parameters:
temperature mode: 130°C / 75°C (gas) and 130°C / 100°C (oil)
boiler pressure drop: 1.5 bar
boiler nominal water flow: 550 m3/h (gas) and 1000 m3/h (oil)

The valves with electric motor actuators, with ON/OFF or continuous control, are mounted on hot water and return water pipelines, on the fresh air and flue gas ducts and are controlled by boiler control system. A fan driven by a 160kW inverter has been installed on the burner air supply. Another fan, driven by a 7.5 kW inverter, has been installed on flue gas recirculation duct, to regulate flue gas NOx ratio.

The process signals are acquired through following transmitters:
Pressure and temperature of hot water on boiler’s input and output and before and after ECO
Pressure and temperature of flue gas before and after ECO, and before LUVO
Pressure and temperature of fresh air on fan’s outtake
flue gas oxygen ratio (O2)
water flow at return pipeline
The control system includes several loops:
burner output loop based on output water temperature (set by SCADA)
fresh air temperature in burner’s intake loop; actuator is air valve
boiler input water temperature loop; actuators are recirculation pump run by inverter or control valve
boiler water flow loop; actuator is control valve
„Mikro Kontrol“ has designed, manufactured and wired the following distribution panels:
The control system panel, consisting of PLC panel (in the boiler room) and HMI panel (in the operator room)
Common consumption distribution panels
Field equipment local panels for actuators – valves

For the new boiler „Mikro Kontrol“ designed, mounted cable trays, laid and connected both signal cables and power cables; the lighting, lightning protection and fire detection equipment were delivered, mounted and wired; sensors were delivered and wired both for boiler and for burner. Mikro Kontrol conducted the appropriate measurements and has provided required certificates.

Control system is based on Omron PLC CJ2, 10’’ HMI and supervisory and control SCADA system developed in Yokogawa Fast/Tools software. Fast/Tools SCADA system performs process visualization, measurements and events archiving, pre-defined or custom reports generation, trends and allows control of actuators and loops of boiler 35MW system. Yokogawa Fast/Tools SCADA application is designed as client / server architecture allowing management personnel to monitor heating plant processes on PCs, tablets, or smartphones.

During control system realization, Mikro Kontrol engaged following human resources:
detailed and as-built design: one engineer, 45 days’ duration
control panels manufacturing, wiring and testing: four electricians, 20 days’ duration
cable and cable trays installation, field equipment wiring: four electricians, 30 days’ duration
PLC and SCADA application programming: three engineers, 60 days duration

Figure 1: Boiler 35MW


Figure 2: : Boiler 35MW - PI&D scheme


Vase Pelagica 30
11000 Belgrade, Serbia
+381 (0)11 3699 080
+381 (0)11 3699 939
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