SAFETY ISSUES IN SOLID FUEL HEATING PRACTICE IN SERBIA

SAFETY ISSUES IN SOLID FUEL HEATING PRACTICE IN SERBIA

Borivoj LJ. STEPANOV, Momčilo Đ. SPASOJEVIĆ, Aleksandar S. ANĐELKOVIĆ, Đorđije D. DODER, Vladimir RAJS, Željko VLAOVIĆ

49. Međunarodni kongres i izložba o KGH, Beograd, 5–7.12.201849th International HVAC&R Congress and Exhibition, Belgrade, 5–7 Dec. 2018

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FACULTY OF TECHNICAL SCIENCES, NOVI SAD, SERBIA

Problem

•Due to economic situation in Serbia old design solid fuel boilers are being used.

•This design has been developed in 70s, is functioning, is cost-effective, although having lower efficiency and higher emissions then the state-of-the- art boilers.

•Often these boilers are installed in closed hydronic heating systems. This is not in accordance with the safety rules prescribed in standards. This practice can lead to explosions, and to loss of human life and property


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Open questions

•Does PROPERLY functioning safety valve prevent boiler explosion? •Does draught regulator can regulate boiler flow temperature at ALL regimes? •Can boiler be safe without system for removal (dissipation) of EXCESS heat? •Can there be a SAFE installation of boiler in a premises without water supply network access point? •What type of solid fuel boilers CAN be installed in closed heating system?


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Open questions

•Is BOILING allowed in closed system?

•Can we treat SAFETY as optional?

•FREQUENCY of heating boiler explosions?


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Old style boiler installed in closed heating system


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Elements of the closed heating system


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Picture from broshure Centrometal BIO-CET


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Steam explosion with overheated water(300 °F -148 °C) (75 psi – 5,2 bar)


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Vessel rupture when temperature of the water is under 100 °C (500 psi = 35 bar)


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BLEVEboiling liquid expanding vapor explosion


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Answers to Open questions

•Does PROPERLY functioning safety valve prevent boiler explosion? •No, it regulates pressure, it does not control the removal of excess heat. 1/20th of the overheat is removed.•Additionaly, it is projected to 110 °C.•Additionaly, system goes toward the boiling.•Does draught regulator can regulate boiler flow temperature at ALL regimes? •No, it regulates temperature in common changes which depend on atmospheric changes, which are slow. In case of electricity, power failure, air lock, it can not regulate temperature.


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Temperature regulator (or draught regulator)


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Answers to Open questions•Can boiler be safe without system for removal (dissipation) of EXCESS heat? •It can if it passes the test, and it fits into category of with rapidly disconnecting firing system. Unfortunately, these are rare in Serbia.•Can there be a SAFE installation of boiler in a premises without water supply network access point? •Similar answer as the previos one. If safety heat exchanger is needed, then water access point is necessary.•What type of solid fuel boilers CAN be installed in closed heating system? •Pellet boilers can, for example. If they pass the test.


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Answers to Open questions

•Is BOILING allowed in closed system?•No, therefore there is a safety temperature difference, and control of temperature. Heating boilers should be called Heating non-boilers.•Can we treat SAFETY as optional?•No.•FREQUENCY of heating boiler explosions?•Low. But we are designing a boiler for worst case scenario.


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Overheating should not be downplayed. Overheating in a closed system is a near explosion situation and it should be treated as such. So systems that prevent it cannot be optional.

CONCLUSIONS


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On the other hand a number of components in the system are working against overheating so frequency of explosion occurrence is low. There must be a perfect storm of failures to result in explosion.

CONCLUSIONS


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Our job as engineers is to apply all known rules. Standard clearly states: “Boilers with manual stoking shall be designed in such a way that, when the boiler is operated in accordance with the boiler manufacturer’s operating instructions, the operator does not run the risk of a hazardous operation mode”. So far the practice was such that played the probability card, and if there comes to explosion escape goat was safety valve.

CONCLUSIONS


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-Special gratitude to then third year students for doing the survey on solid fuel boilers in closed heating systems:

Semester 2016/17; Racić, Gagić, Jakovljević, Milošević, Oluški, Subić, Tojaga, Tomić, Vujanović and Jeremić .

Semester 2017/18; Đukić, Radanović, Bartula, Jovanov, Miletić and Zeljković.


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SAFETY ISSUES IN SOLID FUEL HEATING PRACTICE IN SERBIA