Problematika využití bionafty jako paliva pro stacionární jednotky malých výkonů

Obstacles in the Utilization of Biodiesel as the Fuel in Small Stationary Combustion Units

článek v časopise - ostatní, Jost

en

The presented paper deals with the obstacles in the utilization of biodiesel in small stationary combustion units. The aim of the paper is to discuss the technical problems related to the combustion of biodiesel by means of two different types of atomizers, namely the pneumatic effervescent atomizer and the pressure spill-return swirl atomizer. The technical problems are described based on the comparative combustion tests that were carried out at the nominal heat duty about 1000 kW. The tests were carried out at the experimental burner testing facility, whose main apparatus is the water-cooled combustion chamber. The first part of the paper describes the influence of the physical-chemical properties of the methylester of rape seed oil (RME) on the quality of combustion. The properties of RME are compared to the physical-chemical properties of the most commonly used standardized liquid fuel in small stationary combustion units, namely extra light heating oil (ELHO). There were identified two properties of the RME, namely the flash point and the shape of distillation curve, which cause the problems with the combustion stability by the application of both mechanisms of the atomization. The results of the combustion tests showed that it is required to preheat the RME at the temperature higher than 60 stC and it is useful to use a small gas stabilization burner to stabilize the spray ignition in close proximity of the atomizer head. The next increase of the preheating temperature above 80 stC leads to the significant increase in nitrogen oxides formation, however simultaneously, the stability of the flame becomes better and the carbon monoxide formation decreases. The negligible difference between ELHO and RME was observed in the heat transfer rate to the water-cooled chamber shell. On the other hand, the problems related to the RME spray drops evaporation causes that the maximum heat transfer shifts in the direction further from the burner mouth. The second part of the paper is aimed at the assessment of the possibility of the substitution of the ELHO by RME or some of the vegetable oils from the general view. It may be concluded that the requirements on the RME combustion are evidently harder than for ELHO. It mainly concerns the quality of atomization and the quality of mixing of fuel drops with the oxidizer. Generally speaking it would be better to focus the research on the development of the pressure atomizer and on the decrease of the burner nominal heat duty to the range between 200 and 500 kW. This fact is related to the possibility to utilize these fuels at the decentralized units and/or as the stabilization fuel during the combustion of renewable solid fuels or waste. It is not recommended to use renewable liquid fuels as the main fuel at the large stationary combustion units since it could cause their shortage in other areas of economy.

Cílem článku je rozbor technických problémů při spalování bionafty s využitím dvou typů atomizérů – tlakového atomizéru a effervescentního atomizéru. Rozbpr je založen na provedených zkouškách spalování provedených při nominálním výkonu kolem 1000 kW. Testy byly provedeny s využitím dvopalivového hořáku, vodou chlazené spalovací komory a dalšího příslušenství. První část článku se zaměřuje na popis vlastností metylesteru řepkového oleje (MEŘO) důležitých z hlediska spalování. Vlastnosti MEŘO jsou srovnány s vlastnotmi standartních kapalných paliv, konkrétně extra lehkou topnou naftou (ELTO). Halvní rozdíly byly identifikovány v rozdílném bodu vzplanutí a tvaru destilační křivky, které způsobují problémy se stabilitou plamene při použití obou typů atomizérů. Výsledkem testů je zjištění, že MEŘO je pro spalování nutné předehřát na teplotu alespoň 60 stC při použití plynového stabilizačního hořáku. Předehřev MEŘO na teplotu vyšší než 80 stC způsobuje významné zvýšení koncentrace NOx, avšak stabilita hoření je při vyšších teplotách větší a koncentrace CO ve spalinách naopak klesá. Významnný rozdíl mezi použitím ELTO a MEŘO bylo také v tepelném toku do stěn vodou chlazené spalovací komory. Z důvodu horších rozprašovacích vlastností MEŘO se oblast maximálních teplotních toků posunula směrem od ústí hořáku. V další části článku je posouzena nahraditelnost fosilních kapalných paliv biopalivy vyrobenými z řepkového oleje z obecného hlediska. Je evidentní, že spalování biopaliv je technicky náročnější klade větší nároky na parametry spalovacího zařízení. Celkově bylo konstatováno, že kapalná biopaliva jsou vhodná spíše pro jednotky malých tepelných výkonů v rozmezí 200 až 500 kW. Z tohoto důvodu se jeví MEŘO vhodné především pro decentralizovanou výrobu tepla a elektrické energie a jako palivo pro spoluspalování společně s fosilními palivy.

The presented paper deals with the obstacles in the utilization of biodiesel in small stationary combustion units. The aim of the paper is to discuss the technical problems related to the combustion of biodiesel by means of two different types of atomizers, namely the pneumatic effervescent atomizer and the pressure spill-return swirl atomizer. The technical problems are described based on the comparative combustion tests that were carried out at the nominal heat duty about 1000 kW. The tests were carried out at the experimental burner testing facility, whose main apparatus is the water-cooled combustion chamber. The first part of the paper describes the influence of the physical-chemical properties of the methylester of rape seed oil (RME) on the quality of combustion. The properties of RME are compared to the physical-chemical properties of the most commonly used standardized liquid fuel in small stationary combustion units, namely extra light heating oil (ELHO). There were identified two properties of the RME, namely the flash point and the shape of distillation curve, which cause the problems with the combustion stability by the application of both mechanisms of the atomization. The results of the combustion tests showed that it is required to preheat the RME at the temperature higher than 60 stC and it is useful to use a small gas stabilization burner to stabilize the spray ignition in close proximity of the atomizer head. The next increase of the preheating temperature above 80 stC leads to the significant increase in nitrogen oxides formation, however simultaneously, the stability of the flame becomes better and the carbon monoxide formation decreases. The negligible difference between ELHO and RME was observed in the heat transfer rate to the water-cooled chamber shell. On the other hand, the problems related to the RME spray drops evaporation causes that the maximum heat transfer shifts in the direction further from the burner mouth. The second part of the paper is aimed at the assessment of the possibility of the substitution of the ELHO by RME or some of the vegetable oils from the general view. It may be concluded that the requirements on the RME combustion are evidently harder than for ELHO. It mainly concerns the quality of atomization and the quality of mixing of fuel drops with the oxidizer. Generally speaking it would be better to focus the research on the development of the pressure atomizer and on the decrease of the burner nominal heat duty to the range between 200 and 500 kW. This fact is related to the possibility to utilize these fuels at the decentralized units and/or as the stabilization fuel during the combustion of renewable solid fuels or waste. It is not recommended to use renewable liquid fuels as the main fuel at the large stationary combustion units since it could cause their shortage in other areas of economy.

atomizace, spalování, MEŘO, biopaliva

atomization, biofuels, RME, combustion

2012

25.08.2012

AIDIC Servizi S.r.l.

Milano, Italy

1974-9791

29

2

961–966

6