LABORATORY OF COMBUSTION AND FUELS

Transcription

1 1. Introduction LABORATORY OF COMBUSTION AND FUELS 1.1. 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. 1. 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. 2.). The length of each stage depends on the particle size, the conditions of the combustion, and the properties of coal (composition, structure). Fig. 2. Stages of single coal particle combustion (with smudge photography of burning coal particle) prepared by: P. Kobel; last rev.: p. 1/6

2 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. 3. System for coal burning: a) fixed bed, b) moving grate, c) fluidized bed, d) pulverized coal burner p. 2/6

3 1.4. Pulverized coal burners and furnaces The following types of pulverized coal burners can be distinguished: Considering the air flow and mixing with coal (fig. 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. 4. Pulverized coal burners Considering the location of the burners in the furnace (fig. 5.) a) wall-placed, b) roof-placed, c) corner-placed (tangential firing) Fig. 5. Location of pulverised coal burners in furnace p. 3/6

4 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. 3. 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 fuel carrying air C A electric air heater power supply for heaters with temp. control fluidizing air p. 4/6

5 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 4. Results processing 4.1. 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) 4.2. Calculation of the normalized values of carbon monoxide content and nitrogen oxide content (reference level of oxygen = 6%) CO 6% 6 = CO O 2 NO 6% 6 = NO 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) p. 5/6

6 4.3. 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) 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 p. 6/6