Temperature and pressure effect on gasification process

Temperature and pressure effect on gasification process MAREK BALAS, MARTIN LISY, JIRI MOSKALIK Energy institute Brno University of Technology, Faculty of mechanical engineering Technicka 2, 616 69 Brno CZECH REPUBLIC balas.m@fme.vutbr.cz Abstract:Gasification is among technologies that allow the use of fuel to produce power and heat. This technology is also suitable for biomass conversion. And the use of this renewable source is used to diversify the energy mix and thus the Czech Republic reduces its dependence on fossil fuels and imported energy raw materials from abroad. During gasification, biomass is converted into gas that can then be burned in gas burner with all advantages of gas combustion; or used in internal combustion engines. The main task during gasification is to achieve maximum purity and calorific value of gas. These are mainly dependent on the type of gasifier, gasification medium, biomass quality and last but not least, on the very gasification mode. The paper describes experiments investigating the effect of and pressure on the gas composition, low calorific value and tars content. Experiments were performed in atmospheric gasifier in the laboratories of the Energy Institute at the Faculty of Mechanical Engineering, Brno University of Technology. Key-Words: biomass, gasification, tar content, steam, effect 1 Introduction Biomass is one of the most significant renewable energy sources worldwide. This technology has many advantages such as lower negative impact on environment and utilization of extra agricultural land which is not suitable and/or is not required for food production purposes. Recently, renewable energy sources have covered almost 4 % of power production in Czech Republic and biomass holds an irreplaceable place among these sources. There are various possibilities for heat and power production from biomass, ranging from esterification of oils, biogas production and utilization to thermal processes such as pyrolysis, combustion and gasification. Currently, direct combustion is the most widely used method of power production from biomass. It is the oldest method with a well mastered technology; however, processing lines with low capacity are mostly suitable for heat production from biomass and not for the production of highly praised power. Fuel gasification with subsequent utilization of generator gas in cogeneration unit is among other technologies of power production from biomass. Gasification is a relatively new method providing many advantages. Increased efficiency of utilization of energy from biomass, especially power production is a main asset of gasification process. Combustion of produced gas is a more easily controlled process than combustion of solid biomass, thus it decreases production of harmful emissions. Higher efficiency of power production is achieved using gas in gas turbines and steam-gas cycles. In contrast with combustion, gasification also presents lower heat loss and better energy production from fuel [1]. Gasification is a thermo-chemical conversion of organic mass with limited oxygen supply into lower calorific value gas (4-15 MJ/mn3) whose main components include: CO, CO2, H2, CH4, more complex hydrocarbons, N2 and pollutants. Operating s are rather high, commonly 75 up to 1, C. Produced gas is then combusted in boiler or combustion engines (and/or combustion turbines). Using air as gasification medium results in low calorific value of gas (4-7 MJ/mn3) due to dilution of gas with nitrogen (more than 5 %). Using mixtures of air and oxygen and/or steam as gasification medium produces gas of lower calorific value ranging from 1-15 MJ/mn3 [2]. Heat for endothermic reaction is most commonly produced by partial oxidation of gasified material (air or oxygen as gasification medium) or is supplied from ISBN: 978-1-6184-114-2 198

external sources. Main task of gasification process is to transform as much energy from fuel into gas as possible [3]. Quality (lower calorific value, composition), amount produced by means of gasification and amount of pollutants in gas and their composition are among the most monitored characteristics of produced gas. Our research focused on effect of and pressure on quality and composition of produced gas. As you can see for the title of the paper you must use 16pt, Centered, Bold, Times New Roman. Leave one blank line and then type AUTHORS' NAMES (in Capital, 12pt Times New Roman, centered), Department (in 12pt Times New Roman, centered), University (in 12pt Times New Roman, centered), Address (in 12pt Times New Roman, centered), COUNTRY (in Capital, 12pt Times New Roman, centered). Then you must type your e-mail address and your Web Site address (both in 12pt Times New Roman, centered). The heading of each section should be printed in small, 14pt, left justified, bold, Times New Roman. You must use numbers 1, 2, 3, for the sections' numbering and not Latin numbering (I, II, III, ) 2 Methodology of measurements at Biofluid 1 gasification fluid generator Research was performed at Biofluid 1 stand (see Fig. 1) which is equipment with stationary fluidized bed. Fig. 1 Experimental equipment Biofluid 1 Fig. 2Schéme of Biofluid gasifier Simplified scheme of experimental equipment is presented at Fig. 2. Fuel is supplied from fuel storage tank equipped with shovel and is introduced via dosing screw with frequency convertor into reactor. Primary supply of blower compressed air is lead into reactor under the bed, secondary and tertiary supplies are located at two high-rise levels. Produced energogas is stripped of its solid particulate matter in cyclone. Output gas is combusted in burner equipped with stabilization burner for natural gas and individual air supply. Ashes from reactor can be removed from tank located beneath bed. Power based heater for primary air supply is placed behind blower so that impact of air preheating may be monitored. In recent years, filters for research of efficiency of various methods of gas cleaning were attached to basic part of stand. Reactor parameters: Capacity (in produced gas) 1 kw t Fuel demand 15 kw t Wood consumption 4 kg.h -1 Air flow rate 5 m 3 n.h -1 Basic characteristics of operation at fluid generator are described in following respect: Operation of fluid generator after ignition, fluid generator is operated in combustion mode so that its heating is quick. After achieving required gasification s, secondary and tertiary air is supplied into generator and thus produced gas is immediately combusted and consequently heats up the generator. Air ISBN: 978-1-6184-114-2 199

supplies are then shut off and generator is introduced into stable mode for specific and preset gasification. Stable mode is achieved when amount of dosed fuel is not altered, amount of gasified air is even and swings in middle section of gasification generator are stable within narrow range given by gasification. Data entry of gasification process monitored data is continuously recorded by computer in time interval of 1 seconds for each measurement. Following values are monitored: Frequency of convertor of dosing screw so that mass flow rate is determined; Temperature in various parts of equipment which is measured by thermocouples; position of thermocouples is given in detail in scheme at Fig. 2. There are 3 thermocouples along generator top, 1 thermocouple in cyclone, 1 thermocouple in output gas pipe and 1 thermocouple measures of primary air supply. Pressure difference between upper and lower sections of fluid generator (fluid bed); Pressure difference at orifice plate so that gas flow rate is determined; Pressure of the generated gas at the generator outlet and at the fuel storage tank. Other values such as and air moisture, primary air flow rate and its have to be recorded manually. 3 Course experiments Main task of the experiments was to determine dependency of gas quality on pressure and changes in gasifier. Quality of gas was assessed analyzing its composition and lower calorific value. Device based on infrared spectrometry monitored gas composition (CO and H 2 components) online after stabilization of the stand. Gas was also sampled into test-glass in regular intervals. These gas samples were later analyzed in gas chromatograph (H 2, CO, CO 2, CH 4 components). More of required parameters for samples were set later. 4 Results and discussion Dependency of gas composition on and pressure in gasificaiton generator was experimentally monitored. Dependency of gas composition on fluid bed s (T 11 and T 12) and other values was not proved. Quite contrary, as experiment results prove, in freeboard section (T 13) where chemical balance reactions take place is the key for gas composition (see Fig. 3 through Fig. 1). As charts show, increase of results in increase of hydrogen and carbon monoxide share and decrease of carbon dioxide and methane share. This is caused by decreasing speed of methanizing reactions and higher probability of reactions of water gas ( C + H 2O CO+ H 2 ). Analyses of dependency on pressure are limited by the very equipment. While may be set within the range of 1 C, pressure may be regulated only within the range of ca. 2..5 through 19 kpa. This range is rather narrow; however, dependency of increased methane share on pressure may be observed, i.e. dependency contrary to trends. H2 content [%] Fig. 3 Chart of dependency of H 2 content on T 13 H2 content [%] Fig. 4 Chart of dependency of H 2 content on ISBN: 978-1-6184-114-2 2

CH4 content [%] CO2 content [%] Fig. 5 Chart of dependency of CO 2 content on T 13 Fig. 6 Chart of dependency of CO 2 content on pressure CO content [%] Fig. 7 Chart of dependency of CH 4 content on T 13 Fig. 8 Chart of dependency of CH 4 content on pressure Fig. 9 Chart of dependency of CO content on T 13 Fig. 1 Chart of dependency of CO content on pressure N2 content [%] N2 content [%] CH4content [%] CO content [%] CO2 content [%] LHV [MJ/m Fig. 11 Chart of dependency of N 2 content on T 13 LHV [MJ/m Fig. 12 Chart of dependency of N 2 content on pressure Fig. 13 Chart of dependency of lower calorific value on T 13 Fig. 14 Chart of dependency of lower calorific value on pressure ISBN: 978-1-6184-114-2 21

Subsequent analyses of generated gas focused on its lower calorific value. As Fig. 11 shows, increase of results in slight decrease of nitrogen share in the gas. Considering the above mentioned facts (see previous charts), we see increase of combustible component share in the gas and therefore increase of lower calorific value of the gas (see Fig. 13). Dependency of pressure is again contrary to dependency on (see Fig. 12 and 14). Another outcomeof the experimentsis the dependence ofthe quantity andcomposition oftaron the processparametersst11, T13and pressure.thegraphs showthat total amount of tar decreases in dependence on increasing T11.Dependence ont 13is not soobvious,because the group(benzene, toluene, xylene)decreaseswith increasing, however sgrow. There is noticeabledirecteffect ofpressure on theamount of tar-with a higheramount of tarpressureincreases on thelast image. 5 3 1 Fig. 15Chart of dependency of tar content on T 11 5 3 1 76 78 8 82 84 Temperature 86 88 [ C] 62 64 66 68 7 Temperature [ C] Fig. 16 Chart of dependency of tar content on T 13 8 Fig. 17 Chart of dependency of tarcontent on pressure CONCLUSION 1 2 This paper analyzed effect of gasification and pressure on quality of gas generated from biomass. Results clearly prove hypotheses. It was proved that the itself in fluid bed of gasification reactor has no effect on final gas composition whatsoever. However, T 13, i.e. the in freeboard has direct impact on final gas composition. Increase of results in increase of CO and H 2 share, decrease of CH 4 and CO 2 share and increase of gas lower calorific value. Change in pressure has contrary effect. ACKNOWLEDGEMENTS Pressure[kPa] The paper was supported by the grant SVV 212 FSI-S-11-7 REFERENCES [1] LISY M., BALAS M., MOSKALIK J., POSPISIL J. Research in to biomass and waste gasification in atmospheric fluidized bed, 29, Proceedings of the 3rd WSEAS International Conference on Renewable Energy Sources, RES '9, ISBN 978-96-474-93-2 [2] BALÁŠ M., LISÝ M.Vliv vodní páry na process zplyňování biomasy, Acta Metallurgica Slovaca 1/25, Roč. 11, Košice, 25, ISSN 1335-1532 [3] OCHRANA L., SKÁLA Z., DVOŘÁK P., KUBÍČEK J., NAJSER J. Gasification of Solid Waste and Biomass, VGB PowerTech, 24, vol. 84, no. 6, p. 7-74. ISSN 1435-3199 ISBN: 978-1-6184-114-2 22