THE DEVELOPMENT OF THE POTENTIAL AND ACADEMIC PROGRAMMES OF WROCŁAW UNIVERSITY OF TECHNOLOGY

Transcription

1 THE DEVELOPMENT OF THE POTENTIAL AND ACADEMIC PROGRAMMES OF WROCŁAW UNIVERSITY OF TECHNOLOGY Mining and Power Engineering dr inż. Tomasz Hardy (PhD Eng.) Combustion and fuels - laboratory Project co-financed by European Union within European Social Fund

2 Topics of the laboratory classes 1. Structure of gaseous flames 2. Combustion of liquid fuels 3. Combustion of pulverized solid fuels 4. Combustion of biomass 5. Catalytic burning of CO and CH 6. Pyrolysis of solid fuels Materials for theoretical preparation 1. Spalanie i paliwa, ed. by W. Kordylewski, Oficyna Wydawnicza Politechniki Wrocławskiej, Wrocław, 2008 (ed. V) or 2005 (ed. IV) (in Polish) 2. Presentations for the lecture Combustion and fuels available online at (in English) 3. Handbook of combustion, Vol. 1-5, ed. by M. Lackner, F.Winter, A.K. Agarwal, Wiley- VCH Verlag GmbH & Co. KGaA, Weinheim, 2010 (in English) Project co-financed by European Union within European Social Fund 2

3 1. Structure of gaseous flames 1.1. Introduction Basic definitions Combustion an exothermic chemical reaction between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. Combustible mixture a mixture of a fuel and an oxidizer in which combustion is developing after an ignition source vanishes. Ignition the initiation of the combustion process in the combustible mixture. There are two types of ignition: - external ignition, caused by a local source introduced into the combustible mixture (e.g. spark, pilot flame, etc.) -self-ignition, caused by an even rise of temperature in the whole volume of the combustible mixture above a certain value. Flame the zone where the combustion process takes place. Considering the preparation of a combustible mixture, there are two principal types of flames - premixed flame in which the oxidizer has been mixed with the fuel before it reaches the combustion zone, and the flame speed is determined by rules of chemistry - diffusion flame in which the oxidizer combines with the fuel by diffusion and the flame speed is limited by the rate of diffusion Structure of a premixed flame F fuel (gas), A oxidizer (air) Fig 1.1. Premixed and diffusion flame In the premixed flame three zones can be distinguished (fig 1.2): Heating and reaction initiation zone where the oxidation process is initiated by heat and radicals coming from the main reaction zone. This zone ends at the point where the oxidation process takes place spontaneously, which roughly corresponds to the bend point on the temperature curve. Main reaction zone (flame front) where intense reactions of fuel oxidation take place and the intermediate and final products of combustion (including radicals) are formed. This zone is very thin and large gradients of concentration and temperature occur there. After-flame zone where the temperature drops to ambient temperature and the concentration of combustion products tends to reach the background level. When the amount of an oxidizer is not sufficient, a secondary diffusion flame is formed where the products of a partial combustion (e.g. carbon monoxide) are afterburned. Project co-financed by European Union within European Social Fund 3

4 Fig 1.2. Concentrations (C) and temperature (T) versus position (x) in premixed laminar flame: 1 fuel, 2 flue gas, 3 oxidizer, 4 temperature, 5 premixed flame, 6 sec. diffusion flame Structure of a diffusion flame The diffusion flame is formed in the boundary layer between a flammable gas and an oxidizer. Before combustion can occur, gases must be mixed by diffusion. The diffusion can be of molecular or turbulent nature. The intense reaction zone (flame front) of the diffusion flame is located where the ratio of air to fuel is stoichiometric Gas burners Fig Laminar diffusion flame: 1 gas, 2 flue gas, 3 air, 4 temperature, 5 flame A gas burner is a device used to form a flame using a gaseous fuel. The basic function of gas burners are: - to prepare a combustible mixture with a proper air to fuel ratio; - to ensure a continuous ignition of the mixture; - to ensure total and complete combustion of fuel; - to stabilize the flame front; - to provide a desired shape and size of flame; - to provide desired thermal power of flame. Project co-financed by European Union within European Social Fund 4

5 The following types of gas burners can be distinguished: Considering the preparation of a combustible mixture : - premixing burners in which air and fuel are mixed before the outlet of the burner; - diffusion burners in which air and fuel are fed separately and mix at the outlet of the burner or in the combustion chamber; - premix/diffusion burners in which some air is mixed with fuel before the outlet of the burner and the rest of air is fed separately and mixes at or after the outlet. Considering construction : - jet-ejector burner a premixing burner in which air is sucked by gas flowing from the nozzle; - nozzle-mix burners - a premixing or diffusion burner where air is supplied by an additional device (e.g. a fan) Considering gas flow shaping: - jet burner; - swirl burner Aims of the laboratory 1. To become acquainted with the phenomenon of the combustion of gaseous fuels. 2. To observe a gas burner in operation. 3. To measure the temperature and content of the gas inside a flame in order to determine its structure Diagram of the experimental setup [ x ] flame thermocouple gas probe probe positioning digital temp. meter [ t ] air rotameters burner sample of mixture from flame for chromatographic analysis [ c ] combustible gas sample of fresh air/fuel mixture for chromatographic analysis [ c 100% ] 1.4. Results processing Calculation of the content of the combustible gas in the mixture r = q gas q gas + q air Project co-financed by European Union within European Social Fund 5

6 where: r content of the combustible gas q gas volumetric flow rate of gas (dm 3 /h) q air volumetric flow rate of air (dm 3 /h). Because the volumetric flow rate of gas is measured with a rotameter scaled for air, the correction of the result is necessary (using the formula below) ρ air q gas = q gas ρ gas where: q gas real volumetric flow rate of gas (dm 3 /h) q gas measured volumetric flow rate of gas (dm 3 /h) ρ air density of air (kg/m 3 ) ρ gas density of gas (kg/m 3 ). Check if the calculated content of the gas is within the flammability limits (see textbook for reference) Calculation of the burnout degree of gas w c = 1 c 100 % *100 % where: w - burnout degree c the content of combustible gas in a certain point of flame, measured by chromatographic analysis of sample taken from the flame c 100% the content of combustible gas in fresh air/fuel mixture, measured by chromatographic analysis of a sample taken before the burner Preparation of the charts: a) the burnout degree of gas (w) versus the distance from the centre of the flame (x) b) the temperature of a flame (t) versus the distance from the centre of the flame (x) 1.5. Values to be measured 1. Volumetric flow rates of air q air, dm 3 /h & gas q gas, dm 3 /h 2. Content of unburned gas in fresh air/ fuel mixture c 100% 3. Results of probing of flame (see table blow) content of unburned gas x, mm c t, ºC 0 1 distance from the centre of a flame temperature of flame Project co-financed by European Union within European Social Fund 6

7 2. Combustion of liquid fuels 2.1. Introduction Combustion of oil droplets Combustion of liquid fuels is most often based on their atomization (spraying) and then combustion of droplets. Therefore the mechanism of the single droplet combustion (fig. 2.1.) is important. The combustion of liquid fuels can be divided into two phases: evaporation, and then burning vapours. Consequently, the rate of combustion of liquid fuels is determined by the following factors: - the rate of liquid evaporation, depending on the heat flux transferred into the fuel; - the rate of mixing between air and fuel vapours; - the chemical kinetics of fuel oxidation. Fig Diffusion model of single oil droplet combustion: a) flame geometry, b) temperature (T) and concentration of fuel (ε P ) and oxygen (ε U ) Combustion of heavy oil is more complicated because it forms bigger droplets and contains heavier hydrocarbons. First, the lighter fractions evaporate and burn, then the heavier fractions are decomposed and burned and finally the char residue burns Structure of sprayed oil flame Fig Structure of sprayed oil flame: 1 stream of sprayed fuel, 2 zone of evaporation, 3 zone of ignition, 4 zone of combustion of individual droplets, 5 boundary of flame Project co-financed by European Union within European Social Fund 7

8 Atomization of liquid fuels Atomization of liquid fuels into small droplets provides a high intensity of evaporation and therefore intense combustion. Proper atomization is essential for the quality and efficiency of combustion. An improper spraying causes, among others, worse burnout (manifested by increased CO and soot levels). The disintegration of a liquid jet into a number of filaments and then into small droplets, requires the surface tension forces of liquid to be overcome. It may happen in three ways: - by the surface tension between moving liquid jet and steady air which destabilises the jet and causes its disintegration; - by centrifugal forces of swirled liquid jet; - by outer mechanical and electrostatic forces and by supersonic acoustic. Liquid fuel can be sprayed using the following forms of energy (fig. 2.3.): - the energy of pressurized liquid ; - the energy of pressurised additional gas (air or steam); - the mechanical energy of rotation. An atomiser is characterized by several parameters, among which the most important are (fig. 2.4.): - output, kg/s; - the angle of dispersion; - droplets distribution in the sprayed stream. Fig Fluid atomization with different forms of energy Fig Characteristics of an atomizer Project co-financed by European Union within European Social Fund 8

9 2.2. Aims of the laboratory 1. To become acquainted with the phenomenon of combustion of liquid fuels. 2. To observe oil burners in operation. 3. To obtain the characteristics of combustion with respect to the excess air Diagram of the experimental setup measurement of flame temperature measurement of flue gas temperature flue gas exhaust flue gas analyser [O 2] [CO] [NOx] 1. Combustion chamber 2. Oil burner 3. Oil filter 4. Oil tank 5. Measurement of sooting level (Bacharach s method) 6. Probe of flue gas analyser 2.4. Results processing Calculation of the excess air coefficient λ O 2 where: λ excess air coefficient 21 content of oxygen in air (percents) O 2 content of oxygen in flue gas (percents) Calculation of the normalized values of carbon monoxide content and nitrogen oxide content (reference level of oxygen = 3%) 3% 21 3 CO = CO 21 O 2 NO 3% 21 3 = NO 21 O 2 Project co-financed by European Union within European Social Fund 9

10 where CO 3% normalized value of carbon monoxide content (ppm) NO 3% normalized value of nitrogen oxide content (ppm) CO measured value of carbon monoxide content (ppm) NO measured value of nitrogen oxide content (ppm) 21 content of oxygen in air (percents) 3 reference content of oxygen in flue gas (percents) O 2 content of oxygen in flue gas (percents) Preparation of the charts: a) the normalised content of carbon monoxide (CO 3% ) and the normalized content of nitrogen oxide (NO 3% ) versus the excess air coefficient (λ) b) the temperature of a flame (t fl ) and the temperature of flue gas t fg versus the excess air coefficient (λ) c) the sooting level (S) versus the excess air coefficient (λ) 2.5. Table of values to be measured N o temperature flue flame gas t fl t fg composition of flue gas O 2 CO NO sooting level S - C % ppm ppm B 1 2 Project co-financed by European Union within European Social Fund 10

11 3. Combustion of pulverized solid fuels 3.1. Introduction Composition of coal Basically coal consist of three components: - combustible organic matter, containing carbon, hydrogen, oxygen, sulphur, nitrogen and traces of other elements; - moisture; - mineral matter (ash). Composition of coal is described by: - technical analysis, which determines the content of moisture (W), ash (A) and volatile matter, it also determines the caloric value of coal; - elemental analysis, which determines the content of C, H, O, N, S and other elements Combustion of a coal particle Fig Composition of coal After getting into a flame, a coal particle is heated and dried, then the evaluation and combustion of the volatile matter takes place and finally the burning of char (fig. 3.2.). The length of each stage depends on the particle size, the conditions of the combustion, and the properties of coal (composition, structure). Fig Stages of single coal particle combustion (with a smudge photography of a burning coal particle) Project co-financed by European Union within European Social Fund 11

12 Processes occurring during the combustion of a single coal particle can be divided into two groups: physical, such as: - evaporation of water (drying), - swelling (dilation) of coal particles, - formation of porous structure of char, - physical transformation of mineral matter; chemical, such as: - pyrolisis of coal, - combustion of volatile matter, - combustion of char, - chemical transformation of mineral matter Basic coal combustion systems The most common systems for coal combustion are: - a furnace with a grate (steady or moving); - a fluidized bed furnace (bubble or circulating bed); - a pulverized coal furnace. Others systems are: - a cyclone combustion chamber; - a retort furnace; - a rotary furnace. Fig System for coal burning: a) fixed bed, b) moving grate, c) fluidized bed, d) pulverized coal burner Project co-financed by European Union within European Social Fund 12

13 Pulverized coal burners and furnaces The following types of pulverized coal burners can be distinguished: Considering the air flow and mixing with coal (fig 3.4.): a) a jet burner, designed for the combustion of lean hard coal with a low content of volatile matter (<20%) or lignite and young hard coal with a high content of volatile matter; b) a swirl burner designed for the combustion of fat hard coal with 17-40% volatile matter; a) b) Fig Pulverized coal burners Considering the location of the burners in the furnace (fig. 3.5.) a) wall-placed, b) roof-placed, c) corner-placed (tangential firing) Fig 3.5. Location of pulverised coal burners in the furnace Project co-financed by European Union within European Social Fund 13

14 3.2. Aims of the laboratory 1. To become acquainted with the phenomenon of combustion of solid fuels. 2. To observe a dust burner in operation. 3. To observe a fluidized bed furnace in operation. 4. To measure pollutants emissions from combustion of solid fuel Diagrams of the experimental setups A setup for the observation of a dust flame and measurements of temperature measurement of temperature with thermocouple measurement of temp. with pyrometer C to fume extractor burner air + dust dust container outlet of fume samples air gas Task to do: Compare the temperatures of the flame measured with a thermocouple and a pyrometer and explain why they are different. flue gas probe to fume extractor cyclonic separator A setup for the observation of combustion in the fluidized bed furnace [O] [CO] [NOx] [SO] flue gas analyser fluidized bed furnace, electrically heated return of dust from separator fuel feeder power supply for feeder fuel carrying air C A electric air heater power supply for heaters with temp. control fluidizing air Project co-financed by European Union within European Social Fund 14

15 dust burner Palnik pyłowy fuel (in form of dust) and primary air rozdrobnione paliwo stałe (węgiel, biomasa) powietrze wtórne secondary air A setup with the drop furnace for measurements of emissions electrically heated drop furnace wyciąg spalin to fume extractor power supply (with temp. control) for the heaters of the furnace 8 8 dust separator pyłu separator analizator spalin flue gas analyser 3.4. Results processing Calculation of the excess air coefficient λ O 2 where: λ excess air coefficient 21 content of oxygen in air (percents) O 2 content of oxygen in flue gas (percents) Calculation of the normalized values of carbon monoxide content and nitrogen oxide content (reference level of oxygen = 6%) CO 6% 21 6 = CO 21 O 2 NO 6% 21 6 = NO 21 O 2 where CO 6% normalized value of carbon monoxide content (ppm) NO 6% normalized value of nitrogen oxide content (ppm) CO measured value of carbon monoxide content (ppm) NO measured value of nitrogen oxide content (ppm) 21 content of oxygen in air (percents) 6 reference content of oxygen in flue gas (percents) O 2 content of oxygen in flue gas (percents). Project co-financed by European Union within European Social Fund 15

16 Preparation of charts showing the normalized content of carbon monoxide (CO 6% ) and the normalized content of nitrogen oxide (NO 6% ) versus the excess air coefficient (λ) 3.5. Table of values to be measured N o mass flow of fuel vol. flow of air composition of flue gas O 2 CO NO - g/s l/h % ppm ppm Project co-financed by European Union within European Social Fund 16

17 4. Combustion of biomass 4.1 Introduction The recent years have brought about some climate changes, which may be caused by the constant growth of the amount of carbon dioxide in the air. CO 2 as a greenhouse gas plays the main role in the absorption of heat radiation. This phenomenon may find its reason in a constant growth of fossil fuels consumption. In order to reduce the future growth of CO 2 concentration, the use of renewable energy should be increased. One possibility could be increasing the participation of biofuels in the general fuel balance, with a special emphasis on producing heat energy in small holdings. Biomass absorbs carbon dioxide during growth, as such biofuels are regarded as neutral in CO 2 emission. The main components of wood are: cellulose (45-55wt%), hemicellulose (12-20wt%) and lignins (20-30wt%). Moreover, it includes resins, tannins, fats, proteins and mineral substances. The main components of wood are carbon (50%), oxygen (43%) and hydrogen (6%). Wheat and rape straws contain slightly less carbon, 45% and 47% respectively. Biomass contains small amounts of sulphur compounds, max. 0.5% (wt% of dry fuel). In comparison the dried coal substance contains % (wt% of dry fuel). In the ash from biomass combustion the amount of K 2 O content (4-48wt% of dry ash) was noted to be significantly lower compared to coal burning (2-6 wt% of dry ash). The amounts of the Al 2 O 3 and Fe 2 O 3 were noted to be approximately twice lower. Biomass contains also chlorine - while wood contains little of it (approx. 0.01wt% of dry fuel), straws contain more (rape straw 0.63 and wheat straw wt% of dry fuel). The high content of chlorine is the reason for exploitation problems of boilers, which is chloride corrosion. Even if biomass does not contain chlorine, high levels of potassium in ligninocellulose biomass ash cause increased slugging. This may intensify the corrosion and proper boiler functions may be impaired. Similarly to other solid fuels, biomass combustion consists of three stages: drying and preheating of a fuel; pyrolytic release of volatile flammable gases; combustion of pyrolytic gases and solid residue tar and char. Biomass thermal decomposition starts above 220 C. Individual components subject to decomposition at C for hemicellulose, C for cellulose and C for lignin. Combustion technology and conditions, furnace construction and fuel quality affect the composition of pollutants emitted during wood combustion. Biomass generally has a lower heating value (14-21 MJ/kg) than coal (23-28 MJ/kg) due to its higher moisture. The higher amount of organic matter content in biomass causes lower ignition temperature (for biomass C and for coal C). Biomass combustion and co-combustion with coal helps to reduce most of the gaseous pollutants emissions such as CO, CO 2, NO x and SO 2. Fig Phases of wood combustion Project co-financed by European Union within European Social Fund 17

18 Sources and use of biomass According to Directive 2001/77/EC, biomass is the biodegradable fraction of products, waste and residues from agriculture (including vegetal and animal substances), forestry and related industries, as well as the biodegradable fraction of industrial and municipal waste. Biomass can be obtained from: - agriculture and agri-food industry residues: straw, hay, husks, shells, seeds, pomace, etc.; - energy crops (willow, rose, sunflower, miscanthus, prairie cordgrass and many others); - forest wood and residues from wood, furniture and paper industry; - residues from gardening and other wood or plants residues; - residues from animal breeding (manure) and meat industry (fat, bones, etc.). Biomass can be used for energy generation in the following ways: - by direct combustion (often after drying and fragmentation) also in a compressed form (pellets, briquettes) - by gasification and then combustion of gas - by fermentation and then combustion of gas (bio-gas) - by conversion into liquid fuels (oils, esters, alcohols) and their combustion Aims of the laboratory 1. To become acquainted with the phenomenon of the combustion of biomass. 2. To observe a biomass-fired boiler with a retort furnace in operation. 3. To obtain characteristics of combustion with respect to the excess air Diagram of the experimental setup 1) stack; 2) expansion vessel; 3) pressure gauge; 4) exhaust pipe; 5) boiler controller; 6) fuel container; 7) air heater; 8), 9) water thermometers; 10), 11) pressure gauges;12) pump;13) boiler; 14) air fan; 15) screw feeder; 16) motor; 17) exhaust gas analyzer; 18) exhaust gas thermometer; 20) flow meter Project co-financed by European Union within European Social Fund 18

19 4.4. Results processing Calculation of the efficiency of the boiler where: η b efficiency of the boiler (percents) m w mean mass flow of water (kg s -1 ) C w specific heat capacity of water (kj kg -1 deg -1 ) t w1 mean temperature of return water (deg) t w2 mean temperature of outgoing water (deg) Q w caloric value of fuel (kj kg -1 ) * B b mass flow of fuel (kg s -1 ) B b = m/ τ m mass of consumed fuel (kg) τ duration of the measurements (s). *The kind of burned biomass and its properties will be given at the laboratory Calculation of the excess air coefficient λ O 2 where: λ excess air coefficient 21 content of oxygen in air (percents) O 2 content of oxygen in flue gas (percents) Calculation of the normalized values of the carbon monoxide content and the nitrogen oxide content (reference level of oxygen = 10%) CO 10% = CO 21 O 2 NO 10% = NO 21 O 2 where CO 10% normalized value of carbon monoxide content (ppm) NO 10% normalized value of nitrogen oxide content (ppm) CO measured value of carbon monoxide content (ppm) NO measured value of nitrogen oxide content (ppm) 21 content of oxygen in air (percents) 10 reference content of oxygen in flue gas (percents) O 2 content of oxygen in flue gas (percents). Project co-financed by European Union within European Social Fund 19

20 Preparation of the charts: a) the normalised content of carbon monoxide (CO 10% ) and the normalised content of nitrogen oxide (NO 10% ) versus the excess air coefficient λ; b) the temperature of a flame (t fl )and the temperature of flue gas (t fg )versus the excess air coefficient (λ) Table of values to be measured N o temperatures water volum. flow of water outgoing return flue gas t fg flame t fl composition of flue gas O 2 CO NO - m 3 /h C % ppm ppm 1 2 Project co-financed by European Union within European Social Fund 20

21 5. Catalytic burning of CO and HC 5.1.Introduction Pollutants generation by internal combustion engines The major pollutants present in the exhaust gases from an internal combustion (IC) engine are CO, NO X, SO 2, hydrocarbons (HC) and soot. The amount of the pollutants depends on the composition of the air/fuel mixture and the engine operating conditions (fig. 5.1.). For λ 1,1 the content of CO and HC in the exhaust gas is minimal but then the amount of NO X reaches the maximum. For λ= 0,8-0,9 the amount of NO X is minimal, but the amounts of CO and HC reach their maximum. It means that these pollutants cannot be decreased simultaneously just by controlling the combustion in the engine. A solution to this problem is to apply a catalytic converter, in which NOx is reduced and CO and CH are oxidated. Fig The relationship between the excess air and pollutants concentrations in a spark-ignition IC engine Fig Car catalytic converter Project co-financed by European Union within European Social Fund 21

22 Construction of a catalytic converter (see fig 5.2.) 1. The core is often a ceramic honeycomb in modern catalytic converters, but stainless steel foil honeycombs are also used. The honeycomb surface increases the surface area available to support the catalyst. 2. The washcoat (usually a mixture of silica and alumina), when added to the core, forms a rough, irregular surface, which has a far greater surface area than the flat core surfaces do. The catalyst is added to the washcoat (in suspension) before being applied to the core. 3. The catalyst itself is most often a precious metal. Platinum (Pt) is the most active catalyst and is widely used. Palladium (Pd) and rhodium (Rh) are two other precious metals applied. Platinum and rhodium are used as a reduction catalyst, while platinum and palladium are used as an oxidization catalyst Three-way catalytic converter (TWC) A TWC has three simultaneous tasks: 1. Reduction of nitrogen oxides: 2NO + 2CO = N 2 + 2CO2 2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O 2 = 2CO 2 3. Oxidation of hydrocarbons to carbon dioxide and water: 2C 2 H 6 + 7O 2 = 4CO 2 + 6H 2 O. To achieve the maximum efficiency of catalytic pollutants removal, the near stoichiometric aif/fuel ratio must be provided(fig.5.3.a)). It is achieved with a system which measures the content of oxygen in flue gas (lambda probe) and controls combustion in an engine (fig.5.3.b)). The efficiency of catalytic converters is >90%. conversion efficiency a) b) Fig a) Optimal air/fuel ratio for catalitic conversion b) Contol system with lambda probe 5.2. Aims of the laboratory 1. To become acquainted with the phenomenon of catalysis. 2. To observe a catalytic converter in operation. 3. To measure the effectiveness of carbon monoxide postcombustion with respect to the amount of additional air introduced into the catalytic converter. Project co-financed by European Union within European Social Fund 22

23 5.3. Diagram of the experimental setup 5.4. Results processing Calculation of the excess air coefficient λ λ O 2 where: λ excess air coefficient 21 content of oxygen in air (percents) O 2 content of oxygen in exhaust gas (percents) Calculation of the normalized value of the carbon monoxide content (both for CO before and CO after ), reference level of O 2 = 3% 3% 21 3 CO = CO 21 O 2 where CO 3% normalized value of carbon monoxide content (ppm) CO measured value of carbon monoxide content (ppm) 21 content of oxygen in air (percents) 3 reference content of oxygen in exhaust gas (percents) O 2 content of oxygen in gas (percents) Calculation of the efficiency of the carbon monoxide postcombustion E CO CO = 1 CO 3% after 3% before where E CO efficiency of carbon monoxide postcombustion CO 3% after normalized content of CO after catalytic conversion (ppm) CO 3% before normalized content of CO before catalytic conversion (ppm). Project co-financed by European Union within European Social Fund 23

24 Preparation of the charts (each chart should contain 3 curves one for each load setting): a) the efficiency of CO content reduction (E CO ) versus the additional air flow (q air ) b) the efficiency of CO content reduction (E CO ) versus the excess air coefficient (λ) c) the temperature of a catalytic converter (t cat ) versus the additional air flow (q air ) 5.5. Table of values to be measured engine load volumetric flow rate of additional air into catalytic converter content of oxygen in exhaust gas before catalytic conversion content of oxygen in exhaust gas after catalytic conversion content of carbon monoxide in exhaust gas before catalytic conversion content of carbon monoxide in exhaust gas after catalytic conversion temperature of catalytic converter P q air O 2before O 2after CO before CO after t kat W l/h % % ppm ppm ºC Project co-financed by European Union within European Social Fund 24

25 6. Pyrolisis of solid fuels 6.1. Introduction Pyrolisis Pyrolysis is a thermochemical decomposition of an organic material (coal, biomass, wastes, etc.) at elevated temperatures in the absence of oxygen. During this process volatile matter and liquids (tar) are released and the solid residue is called char. The process of coal pyrolisis is shown in figure 6.1. The process of pyrolisis and the resulting product depend on the conditions (temperature, pressure) and on the composition of a pyrolised material. The intensity of the volatile matter evaluation and the temperature of thermal decomposition vary strongly for different coals, as shown in figure 6.2. Fig Process of coal pyrolisis Fig Volatile matter evaluation for different coals Pyrolisis plays an important role in combustion as an independent fuel technology and also as a stage of combustion process or gasification process. It is also used in chemical industry Gasification Gasification is a process that converts organic materials (coal, biomass, wastes, etc.) into gas, by reacting the raw material with a gasifying medium (usually steam, oxygen, air). The resulting gas mixture, containing mainly carbon monoxide and hydrogen (and nitrogen if air was used), can be used as a fuel (for gas turbines, IC engines, boilers) or as raw material for a further fuel conversion or chemical processing. Gasification of most of solid fuels has two stages (fig 6.2): - degassing of the solid fuel, - gasification of the char residue. high temperature gas fuel char Fig Stages of gasification gasifying medium Project co-financed by European Union within European Social Fund 25

26 6.2. Aims of the laboratory 1. To become acquainted with the phenomenon of pyrolisis. 2. To observe the pyrolisis process for a selected solid fuel (coal or biomass). 3. To obtain characteristics of a pyrolisis process (temperature and mass loss versus time) Diagrams of the experimental setups Oven supply with a temperature controller 2. Oven for sample heating 3. Basket with a sample 4. Thermocouple 5. Inlet of gas for filling the oven 6. Sample mass measurement 7. Computer for control and result analysis 6.4. Results processing Calculation of the speed of mass loss (a derivative of mass change with respect to time) Preparation of a chart showing the change of quantities listed below with respect to time (each should have its own scale of values) - the temperature of the process - the relative loss of mass - the speed of mass loss - the mass of the sample Determining the content of volatile matter in a sample and the speed of volatile matter evaluation 6.5. Table of values to be measured N o time temperature mass loss of mass - s 1 2 o C g % Project co-financed by European Union within European Social Fund 26