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Scientific Divisions / Laboratory of Combustion Processes (13)

Laboratory of combustion processes (13) 

Laboratory Chief

Dr. Nerijus Striūgas

Breslaujos 3, LT-44403 Kaunas

Phone: +370 (37) 40 18 77+370 (37) 40 18 77
Fax:      +370 (37) 35 12 71
Nerijus.Striugas

Additional information could be found in http://combustion.lei.lt/indexEN.htm or laboratory member Algis Džiugys personal page.  


THE MAIN AREAS OF ACTIVITIES OF THE LABORATORY:
 
                   improvement of efficiency of combustion processes;
                   reduction of atmospheric emissions;
                   development and improvement of burners and fuel atomizers;
                   research of thermal destruction and gasification of solid calorific waste;
                   numerical simulation of granular media and multi-particle systems;
                   environmental impact assessment.
 
Research of the Laboratory of Combustion Processes is carried out in the fields of fuel saving, reduction of environmental pollution, and thermal decontamination of materials.
 
REDUCTION OF NITROGEN OXIDES FROM NATURAL GAS COMBUSTION WITH FLUE GAS RECIRCULATION
 
Directive 2010/75/ES On integrated prevention and control of industrial emissions (pollution) foresees more stringent requirements for environment protection and pollution than those currently in force, especially in relation to reduction of the amount of emissions into the environment; these requirements will come in force on January 1, 2016. For natural gas fuel, starting from 2016, the limits for nitrogen oxides (NOx) are 3.5 times stricter – from 350 to 100 mg/nm3. Burning furnace oil from 2016, norms for nitrogen oxides (NOx) are 2.7 times stricter (from 400 to 150 mg/nm3); for sulphur oxides (SO2) – 8.5 times (from 1700 to 200 mg/nm3); for solid particles – 2.5 times (from 50 to 20 mg/nm3).
 
General view of burner D30 
 

This is a complicated task for the existing burning devices: whether to replace the existing burners with the new ones with little amount of nitrogen oxides, or to install secondary measures for reduction of nitrogen oxides. In order to reduce NOx concentration in combustion zones, it is necessary to avoid maximal temperatures of burning plume (1500–1600 oC). Now, quality enhancement of combustion process using burners of new type with specific peripheral air function and tertiary air injection over the flame dominates. One of less sophisticated measures employed is recirculation of flue gas. Recirculation of flue gas does make a major change in the combustion process; however, by employing it, the concentration of nitrogen oxides in emitted flue gas can be reduced by 20–25%. In order to reduce NOx to a greater extent and achieve 100 mg/nm3, more radical improvements are needed. Although, already several decades ago, reliable catalytic and non-catalytic NOx amount reduction measures have been developed, they hardly find their place in industry due to high investment price and complex control process. Presently, another method has been suggested as well, namely, gradual reduction of NOx generation in the course of the combustion process: that is additional fuel supply into the hottest zone of the flame plume. The research methods chosen by the Laboratory of Combustion Processes employ three NOx reduction means: recirculation of flue gas, local additional fuel supply into the lower burner and gradation of the excess air into the upper burner in respect of the lowerburner. By means of burners with LEI design, 200 mg/nm3 of NOx was easily achieved, and based on the regulation, this that in the future, NOx concentration will have to be reduced to 100 mg/nm3, experiments on improving combustion process in water and industrial boilers have begun. The Laboratory of Combustion Processes set up these goals and began implementing experiments with an elongated rectangular furnace boiler, the power of which ranges from 50 to 70 MW.
 
 
Arrangement of boiler KVGM-100 burners central and peripheral airflows and natural gas 
 
 
In parallel, research with specially designed burners D30 for water boiler KVGM 100 was carried out. It was determined that the latter furnace boiler is highly acceptable for gas combustion: aerodynamics was formed in such a way that gas recirculation could take place in furnace space, for this reason, a longer way of combustion reaction is ensured. Burners designed for water boiler KVGM-100 were given standard D30. These burners have two main features: isolation of central and peripheral air flows and natural gas supply system dispersed through 8 injectors around central air with 7 vents in each injector. The design allowed rotating each injector separately in order to get the best combustion process with minimum excess air ratio and minimal emissions. From the very beginning, these burners were marked by high quality work; therefore, meticulous gas flow supply adjustments were conducted while forming a mode card, after several years since the first operation stage of the burners, when fuel oil or gas were burned. The design of the developed burners ideally corresponds to the geometrical shape of the furnace, i.e., flame plume did not burn the rear screen; the flame performed the turns in the furnace, and the combustion time was maximally long, while concentrations of CO and NOx in the exhaust flue gas were minimal. In comparison to burners of other boilers, NOx emission was more than by a quarter smaller. In one of the largest energy companies in Lithuania JSC Vilniaus energija, which exploits the mentioned water boiler by means of KVGM-100 with D-30 burners, experimental research for reduction of additional NOx by recirculation of flue gas was carried out.
 
 Dependence of changes of nitrogen oxide concentration on boiler load with (blue) and without (black) recirculation 


Since NOx concentration in flue gas emitted by this boiler is no more than 150 mg/nm3 at the maximal load, while in other high-capacity boilers, NOx emission in flue gas reaches up to 200–250 mg/nm3, by additionally injecting flue gas into the airflow, it would be possible to achieve the requirements specified in the new EU directive. After completing experimental testing and obtaining a positive result, it would be possible to avoid additional investment into reduction of NOx by urea. In preparation for these experiments, in the Laboratory of Combustion Processes, combustion is modelled by software Fluent in order to evaluate potential NOx reduction effect by means of flue gas recirculation. By comparing these results with the data presented in the literature and with the results obtained at SC Lietuvos elektrinė, it was determined that at actual recirculation of 20% for the case of natural gas combustion, NOx concentration can be reduced by as many as 30%. It is notable that recirculation flue gas has to be supplied evenly, in flows across the entire air channel cross-section into the airflow supplied for combustion and mixed before achieving burners.
 
 
Fan and flues of flue gas recirculation system VK-5. Design boundaries and project boundaries are marked in red 
 
During experimental testing, the flue gas was injected above air supply vents. In the vent, flue gas would mix with the air, supplied for combustion. The first measurements have already revealed better results than expected, and better results than it was anticipated following the theoretical calculations. Experimental research determined that at boiler load 75 and 95 % and using D-30 burners, JSC Vilniaus energija till 2016 would be able to implement European Parliament and Council directive adopted on November 24, 2010.
Flue gas recirculation system for water boiler No. 5 KVGM-100, object JSC Vilniaus energija, at CHP No. 2 (E-2), Elektrinės str. 2, Vilnius, was evaluated with a gold medal at the contest Lithuanian product of the year 2014.
 
DEVELOPMENT OF INNOVATIVE THERMAL DECOMPOSITION TECHNOLOGY AND ITS APPLICATION FOR UTILIZATION OF SEWAGE SLUDGE (INODUMTECH)
 
In 2014, project under Lithuanian Human resource development action program of the third priority for the period 2007–2013 Improving researchers skills VP1-3.1-ŠMM-10-V Promotion of high international level scientific research funded by EU structural funds continued. Project title Development of innovative thermal decomposition technology and its application for utilization of sewage sludge (INODUMTECH). Project is administered by ESFA. Project was launched in January 2013, duration 30 months, i.e., until July 2015. LEI was allocated 2.259 million LTL.
With the expansion of infrastructure of wastewater collection and treatment, the amount of wastewater treatment sludge proportionally increases. At storage sites, large quantities of sludge are accumulated, and the management techniques used to date are becoming a threat to the environment and contradict the principles of sustainable development. Therefore, effective ways to treat sewage sludge are sought for. One of the innovative residual sludge disposal technologies is gasification. By applying this technology, during thermal decomposition, the valuable product is produced from sludge, i.e., flammable gas that can be used for generation of heat and power. Gasification process is applied not only for reduction of the volume of sludge and extra energy production, but also to reduce environmental pollution.
 
 
LEI manufactured an experimental laboratory device. Its main component is gasification reactor, where thermal decomposition of sludge and its mixtures at the temperature 800–1000 °C takes place 
 
 
 
The project is directly related to waste recycling, development of application of renewable energy sources and the major EU energy and environmental policy objectives: to reduce waste accumulation, increase energy supply security, reduce air pollution and greenhouse gas emissions, enhance competitiveness of manufactured production.
Researchers of LEI developed a 100 kW power experimental laboratory device, the main component of which is gasification reactor (sludge and its mixtures are decomposed at the temperature 800–1000 °C) and plasma gas decontamination equipment with auxiliary systems. Linear plasma generator of 40 kW power with atmosphere pressure and hot cathode was selected as a plasma source. Experimental research on thermal decomposition of sludge and its mixture with wood was performed. In order to determine patterns of fuel humidity, ash content, ash melting and release of volatile substances and influence of the fuel composition on the ash content in fuel, research on thermal decomposition of sludge and wood mixtures was carried out. All the necessary equipment for these investigations and experiments, starting from preparation of granular mixtures and testing their quality to combustion in a separate experimental device, equipped with all the necessary equipment for process efficiency and analysis of emissions into the environment and measurement equipment, was set in the Laboratory.
 
 
Gasification reactor 
 
 
Prototype of sludge utilization was developed, and it is widely disseminated in order to attract possible Lithuanian and/or foreign investors, interested in creating commercial size operable prototype, suitable to utilize the amounts of sludge accumulated in small Lithuanian towns.
 
Comparison of gasification of various types of fuel
 
Parameters
Various wood chips
Conifer pellets
Straw granules
Poultry house granules
Sludge and sawdust granules
Sludge and wood pellets
Fuel flow, kg/h
63
57
47
30
28
50
Air flow, Nm3/h:
61
55
49
55
49
57
                      Primary
30
30
30
30
30
30
                      Seondary
 5
 5
 5
 5
 5
 5
                      Tertiary
26
20
14
20
14
22
Excess air coefficient ()
0.21
0.20
0.29
0.41
0.39
0.24
Gas, Nm3/h
130
122
109
90
87
113
Gas output, Nm3/kg
2.06
2.14
2.32
3.00
3.11
2.26
Average gas composition, volume %:
 
 
 
 
 
 
                      H2
16.40
14.01
14,43
14.55
14.00
10.37
                      CO
22.60
24.27
14.59
17.42
16.40
19.01
                      CH4
 4.80
 4.12
 4.06
 1.29
 1.05
 7.14
                      C2H2
 0.11
 0.13
 0.09
 0.07
 0.06
 0.10
                      C2H6
 0.08
 0.11
 0.06
 0.04
 0.05
 0.08
                      C3H8
 0.06
 0.03
 0.03
 0.03
 0.02
 0.06
                      CO2
11.05
10.26
11.8
13.51
 9.20
10.10
                      N2
44.90
47.07
54.96
53.09
59.22
53.14
Lower gas calorific value, MJ/Nm3
 6.50
 6.21
 4.97
 4.32
 4.04
 6.23
Exhaust of ash, kg/h
 3
 6
 6
 2.5
 4
 5
Amount of carbon in ash, %
82.10
84.32
55.43
32.41
34.92
42.76
Tar, g/Nm3
 0.43
 3.31
 0.41
 1.11
 1.24
 2.15
Gas velocity, m/s:
 
 
 
 
 
 
                      In outfall
2.72
2.55
2.28
1.88
1.82
2.37
                      In reduction zone
0.51
0.48
0.43
0.35
0.34
0.44
Cold gas effectiveness, %
82.7
75.1
75.3
80.7
75.4
82.7
Hot gas effectiveness, %
90.4
81.7
83.7
90.8
86.2
89.8
Volumetric load, MW/m2
19.78
17.68
13.00
9.57
8.85
16.42
 
 

 
Investigated fuel types: A – wood chips (WC); B – wood pellets (WP); C – straw granules (SG); D – poultry house granules (PG); E – sludge and sawdust granules (SSP); F – sludge and wood pellets (SWP) 
 

 
 
 
 Temperature distribution in the reactor 
 
 
 
 
 
  

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