Development of tar sampling system - 1 -
1. Tar sampling according to CEN/TS 15439:2006
Installation The installation should be as shown in the figure. There is a pipe in the flange in case the sample should be vented back to the main pipe. Currently it is brought outside the building. Materials At least six impinger bottles, 250 ml, Pirex Quickfit MF 24/5 and 34/35, with plastic clamps. Tubing or glass connections to connect the bottles. Special connection to connect to the metal sampling pipe. Two baths, one with temperature control and the other one to be used just as a contained for dry ice. Isopropanol 99 %. Dry ice. Acetone. Thermometer to read temperature at 20 C. Vaseline - 1 -
Test record Date: Gasification conditions Feedstock: Wood pellets Operators: Mode Gasifier in stand-alone mode. Pyroformer coupled to gasifier Sampling parameters Impinger bottles: Six 250 ml bottles (std. set up) Deviation from the standard: Temp. of the heating tape is below 350 C Sampling nozzle does not turn over Flowrate is above 0.6 m n3 /h (10 l n/min) No glass frits in the bottles Particles not sampled No thermopar at the inlet Sampling point: - Between the candle filter (10 microns) and the scrubber - Temperature of the gas: C - Flowrate of the gas: m n3 /h - Relative pressure: mbar - Absolute pressure: mbar Heating tape: C (set point at 350 C) Results from sampling: Duration: Flowrate: min l n/min Volume: Analysis of gravimetric tar Date: Name: Time: Unusual features: Results (mg/m n3 ): Analysis of GC-detectable tar Date: Name: Time: Unusual features: Results: - 2 -
Methodology 1. Reactants and materials Clean the glassware and connect the bottles. Use a laboratory detergent first, followed by an annealing treatment (500 C for 2 h) Put 150 ml of isopropanol in the first bottle, and 100 ml in bottles 2 to 5. Last bottle is empty. Fill the baths with water (first one) and dry ice with acetone (second one). Allow for enough time for it to cool down. Stopwatch, recording datasheet, storage bottle (2.5 l), Vaseline, funnel, marker. PPE: CO detector, radio, ear plugs, thermal gloves, goggles, laboratory gloves, half mask respirator, leak detector. Start heating up the sampling line 2. Leak test Close the valves and gently pressurise the sampling train with nitrogen. Close the nitrogen, record the pressure drop and check for leaks. Alternatively: Open the three valves. Switch the pump on. Check leaks with the liquid leaks detector. Stop the pump. Close the three valves. NOTES. The pump can never be on with valves closed. Specially no overpressure can be created after the pump (never close the last valve with the pump on) - 3 -
3. Sampling procedure Make sure the heating tape is at 350 C before opening the valves. Make sure the baths temperature is correct (35C - 40C; -15C to -20C). Start filling up the recording data sheet. Open all the valves: (1) on/off valve (2) needle valve at the beginning of the sampling train (3) needle valve at the end of the sampling train; purge valve Record the time and volume (these are the most important readings, at the test start and end) Start the pump and regulate the needle valve (2) to get the required flowrate of 0.6 normal m 3 /h m 3 /h 0.6 0.8 1.0 1.2 1.4 1.6 m 3 /min 0.010 0.013 0.017 0.02 0.023 0.027 l/min 10 13 17 20 23 27 Start filling up the recording data sheets. During the sampling: - monitor the flowrate and adjust the purge valve as necessary to maintain constant flowrate. Flowrate and pressure should be constant to keep isokinetic sampling - occasionally the cooling liquid and the impingers should be agitated to ensure even temperature distribution - when an adequate quantity of tar is collected, or if the pressure drops, the sampling shall be terminated as follows Stop the pump and record the time and volume. Close the valves. Immediately after sampling, the content of the bottles shall be decanted into the storage bottle. Rinse the bottles with solvent and pour the solvent into the storage bottle. Try isopropanol first and, if solid tar residue is observed, use dichloromethane instead (and add it to the storage bottle). Store samples in a labelled, sealed, dark bottles below 5 C until analysis. Analysis should be performed within one month. - 4 -
If the combined sample separates into two or more phases, isopropanol shall be added until it remains homogeneous after stirring. The probe shall be flushed with nitrogen if the probe is not removed. - 5 -
Date: Time: Operator: Tar sampling according to CEN/TS 15439:2006 Time (hh:mm) Volume (m 3 ) Volume flowrate (l/min) Pressure after bottles kpa Temperature after bottles (C) Baths temperature (C) Comments Date: Time: Operator: - 6 -
Time (hh:mm) Volume (m 3 ) Volume flowrate (l/min) Pressure after bottles kpa Temperature after bottles (C) Baths temperature (C) Comments - 7 -
2. Tar analysis according to CEN/TS 15439:2006-1 -
Tar definition Tar is a generic (unspecific) term for entity of all organic compounds present in the gasification product gas excluding gaseous hydrocarbons (C1 through C6). It is thus not correct to give concentration ranges for tar as such. The Technical Specification is designed for measurement of tar in the following concentration ranges: Gravimetric tar 500 mg/m n 3 to 300 g/m n 3 Sum of GC-detectable tars 1 mg/m n 3 to 300 g/m n 3 GC-detectable tar GC-detectable tar is tar that can be measured as a gaseous mixture of individual components according to standard gas chromatographic practice. Gasification tars can be divided roughly into two categories based on tar formation temperature (gasification temperature), namely high temperature tar and low temperature tar. High temperature tar is formed in processes like fluidised bed, downdraft or entrained flow gasification and it contains mainly non-polar aromatic compounds. Low temperature tar is formed at low process temperatures which occur, for example, in updraft gasification processes. The matrix of low temperature tar is highly complex, meaning that the number of individual tar compounds present in gasification product is extremely high. The nature of low temperature tar is also different compared to high temperature tar, as a significant part of low temperature tar consist s of polar compounds. Gravimetric tar Gravimetric tar is the evaporation/distillation residue from particle free sampling solution(s) determined by gravimetric analysis. The concentration range mentioned for gravimetric tar is a ranged based on a sampling time of 2 h. Lower concentration limits can be attained with proportionally longer sampling times: Lower concentration limit of gravimetric tar for different sampling times Sampling time 1 h 2 h 3 h 4 h 5 h 10 h Lower limit, mg/m n 3 1000 500 333 250 200 100 In general, the standard specifies that the total volume sampled must be above 0.1 m n3. For high tar concentration in the gas, duration of sampling can be less than 30 min. For low tar concentration on the gas, extending the sampling time may not be enough to be able to analyse gravimetric tars. - 2 -
3. Commissioning of the tar sampling system - 1 -
1. Introduction According to the technical specification CEN/TS 15439:2006 Biomass gasification. Tar and particles in product gases. Sampling and analysis, a system similar to the one shown in Fig 1 is needed. Figure 1. Modular sampling train. (1) main stream (2) heated sampling probe with on/off valve and control valve (3) heated filter for particles sampling (4) tar collection in impinge bottles (5) volume indication (6) suction pump (7) rotameter and volume meter (8) vent 2. Installation needed 1. Sampling. The sampling point is after the candle filters and before the scrubber. The particles are not going to be sampled, just the tars, so no filter is needed. The flowrate of the gas will be 0.1 0.6 m 3 /h (normal conditions). 2. Nozzle diameter. The nozzle diameter has to be at least 4 mm. It shall be possible to be able to turn the nozzle up and down. 3. Heating tape. For fluidised bed gasifiers, the sampling line should be trace heated to 300-350 C. The gas is at around 200-250 C. A heated line and temperature controller shall be installed. 4. Cooling baths. Impinger bottles are connected as follows: Cooling bath A between 35 and 40 C. Impinger bottles 1, 2 and 4. Cooling bath B between -15 and -20 C. Impinger bottles 3, 5 and 6. EBRI already has two baths, impinger bottles and dry ice. Bottles will be connected in consecutive order using plastic tubing. The baths will be placed in the first floor, by the infrared analyser. - 1 -
F Tar sampling according to CEN/TS 15439:2006 The MicroGC will stay connected in series to the analyser. Otherwise, extra filters and a pump are needed in parallel to the impinger bottles. 5. Chiller. A chiller is needed to achieve the low temperatures required for bath B. Karen Wilson has one we can use, we still may need the right socket in the plant for it. 6. Pump. The pump shall be able to displace 1 m 3 /h at 50000 Pa (normal conditions). This pump is already at EBRI. 7. Volume meter. The results must be given in miligrams of tars per cubic meter of gas. There is a mass flowmeter at EBRI, reading also the gas pressure and temperature. However, the composition should then be used in order to get the gas density and convert the mass flowrate into volumetric flowrate. A rotameter should be used as flow indicator (calibrated for air, 1 m 3 /h). It is recommended but not essential. 8. Other readings. Time, pressure and temperature shalll be read using the following: - Pressure, in the range of 0-1 bar. The mass flowmeter can read pressure, but if it is not installed, a pressure sensor is needed. - Temperature in the water cooling baths: two thermometers are needed, one for 20 C to 100 C and the other one for -20 C to 0 C. - A stopwatch is needed to record the time. Needle valve Rotameter Pressure indicator 0-1 bar I-3 Vent Nitrogen Pump Gas volume meter F Flange in the gasifier pipe On/off valve - Stainless steal pipe -As short as possible, just to reach the first floor 4 10 mm diameter -It shall be possible to turn the nozzle up and down, and indication of its position in the pipe - 2 -
4. Test record - 1 -
Gasification conditions Feedstock: Wood pellets Mode Gasifier in stand-alone mode. Operators: Wehrle and EBRI staff Pyroformer coupled to gasifier Sampling parameters Impinger bottles: Six 250 ml bottles (std. set up) Deviations from the standard: Temp. of the sampling line is below 350 C Sampling nozzle does not turn over Flowrate is above 0.6 m n3 /h (10 l n/min) No glass frits in the bottles Particles not sampled No thermopar at the inlet Sampling point: - Between the candle filter (10 microns) and the scrubber - Temperature of the gas: 173 C - Flowrate of the gas: 560 m n3 /h - Relative pressure: 6 mbar - Absolute pressure: 984 mbar Heating tape: 270 C (set point at 350 C) Results from sampling: Duration: Flowrate: 36 min 23 l n/min Volume: 1.181 m 3 (32.8 l/min) @ 116 kpa, 35C - from the volume meter Volume: 0.828 m n 3 @STP - from the mass flowmeter GC detectable tar: 1 mg/nm3 Gasifier: 200 mg/nm3 Tar concentration, mg/nm3 0.1 10 100 Gas flowrate, Nm3/h 0.6 0.6 0.6 Time sampling, h 1 1 1 Isopropanol volume, ml 300 300 300 Tar in the liquid, mg/ml 0.0002 0.02 0.2-2 -
Date: 29/01/2015 Operator: Clara Serrano Time (hh:mm) Volume (m 3 ) Volume flowrate (l/min) Pressure after bottles kpa Temperature after bottles (C) Baths temperature (C) 14:10 5.924 0 96 29 38-20 Comments 14:15 6.046 23 114 30 38-20 14:20 6.267 23 114 31 38-20 14:25 6.389 23 116 32 38-20 14:30 6.550 23 118 34 38-20 14:35 6.747 23 116 36 38-20 14:46 7.105 23 116 38 38-20 - 3 -
7.2 7 6.8 6.6 6.4 Series1 6.2 6 5.8 14:02 14:09 14:16 14:24 14:31 14:38 14:45 14:52-4 -