Scholarly article on topic 'Design and Development of Downdraft Gasifier to Generate Producer Gas'

Design and Development of Downdraft Gasifier to Generate Producer Gas Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Nikhil Ashok Ingle, Sanjay Shridhar Lakade

Abstract Utilization of waste is the need of hour today. The waste which cannot be degraded by bio-chemical route like agricultural waste, wood waste can be converted into useful fuel through the process called Gasification. Gasification is a thermo-chemical process which converts solid biomass into a mixture of combustible gases that can be used in various applications. In this project, a prototype of downdraft gasifier is designed and developed of 20 KWthcapacity for generating producer gas for fulfilling heating requirement of a heat treatment furnace. Wood blocks of varying sizes are used as a feed stock in the gasifier. The performance characteristics of the gasifier are studied at different air flow rates. A reduction in the overall cost for replacing fuel oil and LPG is estimated. Performance of gasifier with other feed stocks such as agricultural waste briquettes is checked and their results are compared. It is found that wood block of size less than 50 mm has higher calorific value of 3.978MJ/Nm3 and when coconut shells are mixed with wood, the calorific value obtained is highest i.e. 4.865MJ/Nm3.

Academic research paper on topic "Design and Development of Downdraft Gasifier to Generate Producer Gas"

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Energy Procedía 90 (2016) 423 - 431

5th International Conference on Advances in Energy Research, ICAER 2015, 15-17 December

2015, Mumbai, India

Design and development of downdraft gasifier to generate producer

Nikhil Ashok Inglea, Sanjay Shridhar Lakadeb *

aPG student,Pimpri chinchwad college of engineering, University of pune, Pune, India bHead of mechanical department, Pimpri chinchwad college of engineering, University ofpune, Pune, India

Abstract

Utilization of waste is the need of hour today. The waste which cannot be degraded by bio-chemical route like agricultural waste, wood waste can be converted into useful fuel through the process called Gasification. Gasification is a thermo-chemical process which converts solid biomass into a mixture of combustible gases that can be used in various applications. In this project, a prototype of downdraft gasifier is designed and developed of 20 KWthcapacity for generating producer gas for fulfilling heating requirement of a heat treatment furnace. Wood blocks of varying sizes are used as a feed stock in the gasifier. The performance characteristics of the gasifier are studied at different air flow rates. A reduction in the overall cost for replacing fuel oil and LPG is estimated. Performance of gasifier with other feed stocks such as agricultural waste briquettes is checked and their results are compared. It is found that wood block of size less than 50mm has higher calorific value of 3.978 MJ/Nm3 and when coconut shells are mixed with wood, the calorific value obtained is highest i.e. 4.865 MJ/Nm3.

©2016 The Authors. Publishedby Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICAER 2015 Keywords: Biomass, gasifier, producer gas, performance.

1. Introduction

The use of wood to provide heat is as old as mankind, but by directly burning the wood we only utilize about one-third of its energy. Two-thirds is lost into the environment with the smoke. Gasification is the method of collecting the smoke and its combustible components. The laws which govern combustion processes also apply to gasification. The solid biomass fuels suitable for gasification cover a wide range, from wood and paper to peat, lignite and coal. All of these solid fuels are composed primarily of carbon with varying amounts of hydrogen, oxygen and impurities

1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICAER 2015 doi:10.1016/j.egypro.2016.11.209

such as sulphur, ash and moisture. Thus, the aim of gasification is the almost complete transformation of these constituents into gaseous form so that only the ashes and inert materials remain. [1]

Biomass can be formed from living species like plants and animals. Biomass does not take millions of year to develop unlike fossil fuels. Every year, vast amount of biomass grow through photosynthesis by absorbing CO2 from atmosphere. When it burns, it releases the CO2 that the plants had absorbed from the atmosphere recently. Thus, the burning of biomass does not make any net addition to the earth's carbon dioxide levels. Gasification is the thermochemical phenomenon in which chemical transformation occurs along with the conversion of energy. In a sense, gasification is a form of incomplete combustion. Heat from the burning solid fuel creates gases which are unable to burn completely, due to insufficient amounts of oxygen from the available supply of air.

In the gasification process, solid biomass is broken down to produce a combustible gas by the use of heat in an oxygen-starved environment. Heat for gasification is generated through partial combustion of the feed material. The resulting chemical breakdown of the fuel and internal reactions result in a combustible gas usually called "producer gas" [1]. The main combustible gases are H2 and CO, but small amounts of methane, ethane and acetylene are also produced. Overall gasification efficiency is generally dependent on the specific gasifier used, fuel type, fuel moisture content and fuel geometry. Fuel gas from air blown gasifier has low calorific value (around 5MJ/m3) and fuel gas from oxygen fed gasifier has a medium calorific value (10 - 20 MJ/m3). This gas can either be used on site to produce heat, electrical or mechanical energy or can be converted into substitute like methane and methanol.

The main objective of the present work is to design and develop a down draft gasifier that uses wood as a feed stock to generate producer gas which will help to fulfill heating requirement for heat treatment furnaces. An experimental study [2] was carried out on a 75kW downdraft biomass gasifier system to obtain temperature profile, gas composition, calorific value and trends for pressure drop across the porous gasifier bed, cooling-cleaning train and across the system as a whole in both firing as well as non-firing mode. In the reactor, both gas and biomass feedstock move downward as the reaction proceeds. While biomass flows because of gravity, air was injected with the help of a blower. Experiments were conducted to obtain fluid flow characteristics of the gasifier and also to obtain the temperature profile in the reactive bed, the gas composition and calorific value.

An experimental study was carried out on producer gas generation [3] from wood waste in a downdraft biomass gasifier. They used sesame wood or rosewood as biomass. They observed that biomass consumption rate decreased with an increase in the moisture content and it increased with an increase in the air flow rate. The performance of the biomass gasifier system was evaluated in terms of producer gas composition, the calorific value of producer gas, gas generation rate, zone temperatures and cold gas efficiency. Thermocouples were placed inside the gasifier at different locations to measure the temperature of various zones of gasifier. They found the producer gas composition using gas chromatograph.

The paper [4] showed that the thermo-chemical reaction in gasification may vary with varying parameters and the size of biomass. For a particle size below 1mm diameter, thermo-chemical reaction shows a sharp increase in the fuel conversion which could be used in conventional entrained flow gasifier. A reduction in the fuel particle size led to an improvement in the gas quality and thus to a higher producer gas heating value. Maximum fuel conversion was obtained for the smallest particle size tested (0.5mm). The thermo-chemical characterization of the char-ash residue showed that as the fuels particle size was reduced, the release of volatile matter during pyrolysis stage along with particle carbonization, gradually increased, which suggest that pyrolysis reaction took place to a great extent. For fuel particle size of 1mm, the reaction of char gasification became more relevant which contribute in the improvement of conversion of fuel and the composition of producer gas. It is necessary to cool biomass-based producer gas to ambient temperature, and clean it of tar and particulates before it could be used as a fuel. The unit gave a clean gas with tar and dust content below the limit of 150 mg/nm3 as long as the inlet gas tar and dust content was below about 600 mg/Nm3. The system was being tested to supply gas to a dual-fuel engine, and solve any operating problems in this application. It was developed further to study its maintenance requirements, and increase the number of hours of continuous use of the sand filter with no operator attention. The system was mainly developed for small scale gasifier-engine system applications. It can be scaled up to larger sizes to provide a compact unit. The scale up can be done by increasing the cross-sectional areas of the various beds and the water flow rate in proportion to the producer gas flow rate. Here introduce the paper, and put a nomenclature if necessary, in a box with the same font size as the rest of the paper. The paragraphs continue from here and are only separated by

headings, subheadings, images and formulae. The section headings are arranged by numbers, bold and 10 pt. Here follows further instructions for authors.

Nomenclature

LDO light diesel oil

FO fuel oil

SSF specific solid fuel

CV calorific value

2. Experimental Method

2.1. Experimental Setup

The setup was built in company named DECK INDIA Engineering Pvt. Ltd. Fig 1 shows the schematic of the downdraft gasifier. It consists of hopper, reactor, grate, ash handling system, air blower. The hopper is made up of MS material with 650 mm OD and 500mm ID. It is used to hold the biomass into it. The biomass is fed through hopper into the reactor. The reactor is a cone shaped cylinder made up of SS 304 material in which the actual reactions take place. The gas is generated in this region and then comes out from the bottom. The feed material is held on grate also made of SS 304. The remaining ash is collected in the ash pond. Air blower of 1 Hp motor with variable air flow rates is used to provide sufficient quantity of air for combustion. Three air nozzles are provided at 120° each.

Figl. Schematic of gasifier

Table lSpecifications of the different components of the gasifer

Gross Dimensions

Height 1900 mm Diameter 650 mm

Hopper ID 500 mm OD 650 mm Height 800 mm

Reactor Throat Diameter 200mm Height 750 mm

Nozzles Diameter mm 12.5 Nos. 3

Grate Diameter mm 330 Nos. 1

Ash Pond Diameter mm 650

2.2 Experimental Procedure

In the present work K type thermocouples, hot wire anemometer is used to measure temperature and velocities respectively. Gas analyser is used to measure the constituents of the gas. In this work, first the feedstocks used are wood pellets of sizes 100-150 mm, then of size 30-50 mm, and agricultural waste of 70-80 mm.

At the cold start phase, the gas produced initially is of low quality and so it is released to the atmosphere. When the reactor temperature reaches near to 500° C-600° C, sample of gas is checked for the quality. Near about half an hour is required at the initial stage to get a good quality gas continuously. After that the air velocity is checked and maintained for optimum performance.

Fig 2. Experimental setup of gasifier

2.3 Process Technology

The combustible substance of a solid fuel is usually composed of elements carbon, hydrogen and oxygen. The producer gas is formed by the partial combustion of solid biomass in a vertical flow packed bed reactor. In the conventional theory of producer gas, gasification reaction takes place in four zones. They are oxidation, reduction, pyrolysis and distillation zones. The Gasification process technology is based on production of a highly combustible gas by controlled reactions of Biomass viz. rice husk, wood, palm nut shell etc. with air and water vapour. A number of chain chemical reactions are believed to take place in the gas generator from the bottom to the top, a proper

mixture of air water vapours pass through channel free compact fuel bed ensuring the following reactions to take place.

• Oxidation Zone: In the oxidation zone, the oxygen in the air-stream reacts with the carbon and hydrogen in the fuel to reduce carbon and hydrogen to form carbon dioxide and water. Carbon dioxide is obtained from carbon and water is obtained from the hydrogen in the fuel.

C + O2 = CO2 (+393 MJ/kg mole) (1)

2H2 + O2 = 2H2O (-242 MJ/kg mole) (2)

• Reduction Zone: The partial combustion products CO2, H2O obtained from oxidation zone are now passed through reduction zone. Here CO2 and H2O are reduced to form carbon monoxide (CO) and hydrogen (H2) by absorbing heat from the oxidation zone. Oxidation zone raise the temperature of reduction zone to promote the carbon/steam gasification reaction which has higher activation energy. This reaction requires temperature of 9000C and above. Over 90% of CO2 is reduced to CO at temperatures above 900°C. It is an

endothermic reaction.

C + CO2 = 2CO (- 164.9 MJ/kg mole) (3)

C + H2O = CO + H2 (- 122.6 MJ/kg mole) (4)

C + 2H2O = CO2 + 2H2 (-88 MJ/kg mole) (5)

CO + H2O = CO2 + H2 (+42 MJ/kg mole) (6)

C + 2H2 = CH4 (+75 MJ/kg mole) (7)

2.4 Composition of Gas : Though for different biomass fuels, there may be little variation in gas composition as

well as the heating value, the gas composition and calorific value in general are as follows :-

CO2 = 8 ~ 10%, O2 = Less than 1.0%, CO = 24 ~ 26%,

CH4 = 1.5 ~ 2%, N2 = 54 ~ 56%, H2 = 10 ~ 12%.

CV. (Gross) = 1200 ~ 1250 kCal/Normal cubic meter

Sp. Gravity = 0.92

Yield of Gas: 2.0 ~ 2.5 Normal cubic meter per kg of biomass.

2.5 Economic Benefits

• Fuel saving: Switching from furnace oil to biomass generates fuel Replacement of 6588 kg per month of furnace oil with 22 tonnes of wood consumption in gasifier monthly.

• Electricity saving: The new Biomass Gasifier would save 150 units of electricity per month.

• Reduction in other losses: The combustion of producer gas is a more efficient process than burning furnace oil. It reduces the amount of wastage in fuel while performing the process.

• Monetary benefits: The monetary benefits of the unit are mainly due to the lower price of wood chips compared to furnace oil. This amounts to monetary savings of Rs. 75000 /month. A detailed estimate of the saving has been provided in the table 2 below:

Table 2 Energy and monetary benefit

Sr. No Parameter Value

1 Amount of FO used in furnace (kg/hr) 9.15

2 Amount of FO used in furnace (kg/month) 6588

3 Calorific value of FO(MJ/kg) 42.3

4 Cost of FO (Rs/kg) 35

5 Cost of FO in present system (Rs/month) 2,30,580

6 Amount of wood required by gasifier (kg/hr) 30

7 Amount of wood required by gasifier (kg/month) 22,204

8 Cost of wood (Rs/kg) 7

9 Cost of wood for the gasifier (Rs/month) 1,55,433

10 Monetary saving (Rs/month) 75,147

11 Total investment cost (Rs in Lakhs) 1.75 - 2.25

12 Return on investment (months) 4-6

• Reduction in effluent generation: There would be less effluent generation since there would less fuel burned in the furnace.

Producer gas burns more cleanly than furnace oil and produces less ash. The ash produced from wood could be used for fertilizers. Moreover, the generation of dross is reduced due to better temperature regulation.

• Reduction in GHG emission: The measure helps in reducing CO2 emission. The sustainable use of biomass as fuel would have zero net emission of CO2 into the environment.

• Reduction in other emissions like SOX: Significant amount of SOX will be reduced due to application of the bio-gasification process. The corresponding SOX emission would also be reduced.

3. Results and discussion

Experiments were carried out to find out the composition of gas for various feed materials. Also the optimum velocity at which the maximum CV of the fuel will be obtained is found out.

3.1 Effect of Grate design

Grate design is of much importance in designing of gasifiers. Grate is a component which holds the biomass material in it. Grate design and spacing has direct impact on the generation of gas. The gap between rods governs the flow of material downward into the ash pond. Here two different grate designs are tested and the suitable one is adopted. The comparison among the two is done based on the performance and gas quality.

Fig3a. Grate design with gap 25 mm Fig3b. Grate design with gap 12 mm

Figure 3a shows the grate used for the wood blocks of size more than 50 mm and for biomass briquettes. It has gap of 25 mm between each rod. This gap ensures that the ash formed by this feedstock goes smoothly through the grate without any chocking. Figure 3b shows grate with the gap in between the rods 12 mm.

3.2 Gas composition of various feedstocks

Effect of various feedstocks on the composition of gas is obtained and comparison is done. Tests were carried out using three kinds of feedstock, wood pellets, biomass briquettes, and wood pieces. The results are depicted in Fig 4. The graph shows variation of percentage of gas constituents on vertical axis and gas constituents on horizontal axis. It is observed that the CO and H2 content are highest in the gas from wood pieces of size 30-50 mm with coconut shells added to it. These CO and H2 contents are responsible for the calorific valve of the gas. Agricultural waste briquette has lowest content of CO and H2.

s„ p| n n

40% ■ I ■ . CO

;: rJ 1J J J

o% -1-i-

WB (<50mm) WB( 100mm- 150mm) BB

Feed Stocks

Fig4. Gas composition of various feedstock

3.3 Effect of air velocity on CO content

Figures 5a and 5b depicts the effect of air velocity on CO content. As the calorific value of gas is much dependent on CO content, it is convenient to plot variation of velocity with CO contain. Graph shows the percentage of CO on vertical axis and velocity on horizontal axis. It is observed that CO content is highest at air velocity of 2.9 m/s for wood material. Similarly air velocity of 3.88 m/s is optimum for biomass material.

Fig5a. Effect of air velocity on CO content for wood Fig 5b. Effect of air velocity on CO content for biomass

3.4 Comparison of wood with coconut shells

It was found that wood blocks of smaller sizes the 50mm diameter are the most suitable for this gasifier. After this the readings on coconut shells mixed with wood were taken. Coconut shells have much higher content of fixed carbon in it near about 75%. So it was found that the composition of producer gas was even higher in H2 and CO containt than the wood alone. The calorific value obtained is 4.865 MJ/Nm3.

Fig. 6 Comparison of calorific values

4. Conclusions

A downdraft gasifier is designed and experimental study has been carried out to produce the required quality of gas. Following conclusions are made from the experimental study and is detailed below:

• Wood pieces of size 30-50 mm are best suitable as a feedstock than of the size greater than that.

• Calorific value of gas from wood blocks of 100-150mm size is 3.213 MJ/Nm3.

• Calorific value of gas from biomass briquettes is 2.447 MJ/Nm3.

• Calorific value of gas from wood blocks of <50mm size is 3.978 MJ/Nm3.

• Calorific value of gas from coconut shells mixed with wood is CV= 4.865 MJ/Nm3

• Wood has more calorific value than agricultural biomass briquettes as it has more CO and H2 content.

• When coconut shells are mixed in wood its calorific value increases.

• Air velocity of 2.9 m/s is optimum for wood and air velocity of 3.88 m/s is optimum for biomass briquettes.

Acknowledgment

The Authors would like to thank Mr. D. K. Salunkhe, MD of DECK INDIA Engineering Pvt. Ltd. for his valuable support in manufacturing the gasifier.

References

[1] ParbirBasu, "Biomass Gasification, Pyrolysis, and Torrefaction, Practical Design and Theory", Dalhousee University and Greenfield Research Incorporated, Academic Press, Boston, 2013.

[2] Jan Venselaar, "Design rules for downdraft gasifier", Institute of Teknologi Bandung, Indonesia, August 1982.

[3] Sharma K.A. Experimental study on 75 kWth downdraft (biomass) gasifier system, Renewable Energy, 34 (2009), pp. 1726-1733.

[4] ShethN.Pratik, Babu V.B. Experimental studies on producer gas generation from wood waste in a downdraft biomass gasifier, Bioresource Technology, 100 (2009), pp.3127- 3133.

[5] Mohamed Ali Masmoudi, M. Sahraoui, N. Grioui, K. Halouani, "2-D Modeling of thermo-kinetics coupled with heat and mass transfer in the reduction zone of a fixed bed downdraft biomass gasifier", Renewable Energy, vol. 66 (2014), pp. 288-298.

[6] S. J. Ojolo ,J. I Orisaliye, "Design and development of a laboratory scale biomass gasifier", August 31, 2010.

[7] N. Striugas, K. Zakarauskas, R. Paul, "An evaluation of performance of automatically operated multi-fuel downdraft gasifier for energy production", Applied thermal engineering, 73 (2014), pp. 1151-1159.