22nd European Biomass Conference and Exhibition

22nd European Biomass Conference and Exhibition, 23-26 June 2014, Hamburg, Germany

EXPERIENCE OF OPERATING OPEN TOP BIOMASS GASIFIER USING A LOW DENSITY FUEL – COCONUT FRONDS S. Dasappa1, K C Suresh2, D N Subbukrishna2 1 Centre for Sustainable Technologies 2 Combustion, Gasification and Propulsion Laboratory Indian Institute of Science, Bangalore 560 012, India Email: [email protected], Phone : +918023600536, Fax: +918023601692

ABSTRACT: Use of fuel other than woody generally has been limited to rice husk and other residues are rarely tried as a fuel in a gasification system. With the availability of woody biomass in most countries like India, alternates fuels are being explored for sustainable supply of fuel. Use of agro residues has been explored after briquetting. There are few feedstock’s like coconut fronts, maize cobs, etc, that might require lesser preprocessing steps compared to briquetting. The paper presents a detailed investigation into using coconut fronds as a fuel in an open top down draft gasification system. The fuel has ash content of 7% and was dried to moisture levels of 12 %. The average bulk density was found to be 230 kg/m3 with a fuel size particle of an average size 40 mm as compared to 350 kg/m3 for a standard wood pieces. A typical dry coconut fronds weighs about 2.5kgs and on an average 6 m long and 90 % of the frond is the petiole which is generally used as a fuel. The focus was also to compare the overall process with respect to operating with a typical woody biomass like subabul whose ash content is 1 %. The open top gasification system consists of a reactor, cooling and cleaning system along with water treatment. The performance parameters studied were the gas composition, tar and particulates in the clean gas, water quality and reactor pressure drop apart from other standard data collection of fuel flow rate, etc. The average gas composition was found to be CO 15 ± 1.0 % H2 16±1% CH4 0.5 ± 0.1 %CO2 12.0 ± 1.0 % and rest N2 compared to CO 19 ± 1.0 % H2 17 ± 1.0 %, CH4 1 ±0.2 %, CO2 12 ± 1.0 % and rest N2. The tar and particulate content in the clean gas has been found to be about 10 and 12 mg/m3 in both cases. The presence of high ash content material increased the pressure drop with coconut frond compared to woody biomass. Keywords: gasifier, tar and particulate, biomass, downdraft

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worldwide, with a total production of 54 billion nuts per annum. India occupies the premier position in the world with an annual production of 13 billion nuts, overtaking Indonesia and the Philippines, the other two prominent coconut-growing countries. Coconut is grown in more than 93 countries of the world in an area of 12.29 million ha with a total production in terms of copra equivalent of 11.04 million MT. Indonesia (25.63%), Philippines (23.91%), India (19.20%) are the major coconut producing countries of the world. India occupies a predominant position in respect of production of coconut in the world. Coconut is grown in 1.94 million ha in 19 states and 3 Union Territories of the country producing 15730 million nuts with an average productivity of 8303 nuts per ha or 44.27 nuts/palm/year. Traditional areas of coconut in India are the states of Kerala, Tamil Nadu, Karnataka, Andhra Pradesh, Orissa, Goa, West Bengal, Pondicherry, Maharashtra and Islands of Lakshadweep and Andaman and Nicobar. Nontraditional areas are the states of Assam, Gujarat, Madhya Pradesh, Bihar, Tripura, Manipur, Nagaland and Arunachal Pradesh. The four southern states put together account for more than 90% of the total production in the country (Kerala 36.88%, Tamil Nadu 34.11%, Karnataka 13.83%, Andhra Pradesh 6.16% and other states 9.0%) [4]. Four southern states put together account for 92% of the total production in the country (Kerala 45.22%, Tamil Nadu 26.56%, Karnataka 10.85%, Andhra Pradesh 8.93% and other states 8.44%). Coconut is a crop of small and marginal farmers since 98% of about five million coconut holdings in the country are less than two hectares. In the west coast of India, the palm is an essential component in the homestead system of farming. Kerala, which has the largest number of coconut

INTRODUCTION

Use of agro residue as a fuel has been desirable in the thermo-chemical conversion process – both combustion and gasification. Gasification as an energy conversion process has been used extensively for charcoal and woody biomass as fuel, but very little work has been reported for loose agro wastes except rice husk, at small power plant levels (about 1 MWe). Current estimates of the net annual bio-residue availability for power generation in India stands at 100 million tonnes (t) a year amounting to about 15000 MWe capacity [1,2,3]. Typical residues generated from agro industries are rice husk, coconut shell, corncobs, coir pith, tapioca waste, groundnut shells, coffee husk, etc. Bagasse from the sugar industry has a captive use for both heat and electricity. Typically, 5-20 % of the feedstock remains as waste depending upon the industry. Some of these residues are used as fuel in combustion systems either for heat or power generation or a combination of both. The power generation is packaged with steam turbines in the capacity range of 4 MWe and above. The concept of captive power generation using wastes generated in-house is common in industries such as sugar, paper, and rice mills with cogeneration concept in the recent times. Even though there are several case studies where captive power generation systems have been successfully implemented, there is also enough evidence that a large amount of these raw materials is being inefficiently utilized, thus contributing to pollution of the environment. The challenge has been in the usage low high ash content fuel with low ash melting point due to additional inorganics. Both availability of cost competitiveness of woody biomass, being question, various end users are addressing other crop residues as fuel. Coconut is grown in more than 86 countries

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trees, is famous for its coconut-based products—coconut water, copra, coconut oil, coconut cake (also called coconut meal, copra cake, or copra meal), coconut toddy, coconut shell-based products, coconut wood-based products, coconut leaves, and coir pith. Of the various residues, coconut frond is available in abundance in few areas in India and other countries. Very limited usage has taken place in combustion system due to the ash related aspects, and current major use has been in the thatched roof construction and as a shelter material. In recent times, the fronds are also explored as a structural material with requisite treatment process.

kg/m3 and a moisture content after drying was 11 %. Similarly, woody biomass Subabul has a bulk density of 350 kg/m3 and has an ash content of 1.5 %

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Figure 1: Coconut frond and Subabul as the fuel

Coconut frond

MATERIALS AND METHODS

This study addresses usage of raw material is leafy material called frond from the coconut tree for the pur. The typical analysis of this fuel suggests that it has about 6 to 8 per cent ash, about 75 percent volatiles and 20 percent fixed carbon. The average calorific value is about 17 MJ /kg. Further, the elemental composition suggest that the presence of inorganics like K, Ca, etc pose issue related to ash fusion and also contribute to water contamination during scrubbing. The moisture ash content and ash fusion was determined using ASTM D3173-87 ASTM D 3174-89 and ASTM D1857 respectively.

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C O Al Si Cl K Ca Fe Co Zn

RESULTS AND DISCUSSIONS

The gasifier system was operated on both these fuels to compare the operation and the gas quality between these fuels and flaring the gas. Long term experiments suggests that the pressure drop across the reactor for both the fuel. 3.1 Pressure drop across the reactor The pressure drop is an indication of the bed resistance with increased ash content. Figure 2 and 3 show the reactor pressure drop for both the fuel. The pressure drop with coconut frond as the fuel at 130 m3/hr of gas flow rate was in the range of 700 Pa, while for Subabul it was around 300 Pa for the same flow rate. This difference can be attributed to the ash content and its related influence on the bed resistance and also the ash removal system.

Table I: Elemental composition of frond Element

Subabul

Composition of element (% wt) 77.67 42.75 2.63 0.84 0.15 0.16 0.18 0.55 0.34 4.73

A typical gasifier system configuration is shown in Figure 1. The open top downdraft reactor design is made of a ceramic lined cylindrical vessel for improved life in highly corrosive thermal environment inside the reactor along with a bottom screw for ash extraction. In brief the reactor has air nozzles and open top for air to be drawn into the system to help in improving the residence time of the gas and enabling cracking of higher molecular weight compounds. The novelty in the design arises from the dual air entry - air being drawn from top of reactor and as well through the nozzles - permits establishing a flame front moving towards the top of the reactor, thus ensuring a large thermal bed inside the reactor, to improve the gas residence time. The details of the gasification technology are discussed in [5]. An unique screw-based ash extraction system allows for extracting the residue at a predetermined rate. A blower provides necessary suction for meeting the engine requirements. The gas was initially flared and later connected to the engine. Gas composition was measuring using Maihak online gas analyzer. The coconut frond was sized to approximately 40 mm x 40 mm. The average bulk density was found to be 230

Figure 2: Pressure drop across the reactor with coconut frond as the fuel

Figure 3: Pressure drop across the reactor with Subabul as the fuel

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3.2 Tar and particulates in the gas Having ensured the operability of coconut fronds in the fixed bed gasifier another important parameter that had to be measured was the gas quality. The gas quality was checked using wet P and T method at the engine inlet and anisole as the solvent [6]. In brief, gas samples are drawn iso-kinetically from the main gas line. The sampling train consists of sampling bottles containing distilled water ( 1 number), empty bottle (1 number), anisole (3 numbers), maintained in at low temperature (close to freezing mixture) and at the end a thimble filter. The gas sample is drawn through the sampling apparatus and a gas meter using a vacuum pump. The outlet of the vacuum pump is connected to a burner to burn the gas. Amount of gas drawn through this train is obtained from integrated gas flow meter. At the end of the experiment, all the gas line between the valve below the sampling probe and the gas flow line is washed with anisole for any tar/ dust sticking in the line and is added to the tar/dust collected in the cold traps. Tar thus collected is dissolved in anisole and filtered to separate any dust collected along with tar. Soxhlet extraction is carried out to determine the tar and particulate content. The results from the tests are indicated in Table II.Tar content in the cold gas was measured using the wet method with anisole as the solvent, and further analysis was carried out using gravimetric process.

Fuel type

Thimble filter 1m3 of gas

Coconut frond

Subabul

Figure 5: Thimble after passing gas through the solvent bottles Figure 5 shows the thimble used in the tar sampling train. About 1 m3 of gas has been drawn through the thimble under isokinetic condition. From the figure it is evident that the gas is extermely clean in both the cases, suggesting that the reactor as well as gas conditioning equipment is performing well. 3.3 Gas composition The gas composition measurement using online gas analyser (SICK Maihak: S715 Extractive gas analysers) was employed for recording data at periodic time intervals. The tests were conducted at different gas flow rates and the gas composition was measured. Figure 6 and 7 presents results on the gas composition with both the fuels. It is evident that the gas composition is nearly same for both the fuels. The average gas composition was found to be CO 15 ± 1.0 % H2 16±1% CH4 0.5 ± 0.1 %CO2 12.0 ± 1.0 % and rest N2 in the case of coconut frond compared to the one obtained using Sababul as CO 19 ± 1.0 % H217 ± 1.0 %, CH4 1 ±0.2 %, CO212 ± 1.0 % and rest N2.

Figure 6 Gas compostion with coconut fronds as fuel Figure 4 Tar and particulate measuring system Table II: Tar and particulate matter in the cold gas for both the fuels Fuel type Coconut frond Subabul

Tar mg/m3 10.5±1.5 9.87±1.2

Particulate mg/m3 14.2±3.2 12.5±2.5

Table II provides the details on the cold gas analysis for both the fuels. The measurement were made after the filter. In both the cases the tar and particulate content in the clean gas has been found to be in the range of 10 and 13 mg/m3 respectively.

Figure 7 Gas compostion with subabul as fuel

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While the gas composition in the case of Subabul is better than that of Coconut fronds, it is clear that the fronds can be gasified. A water treatment as per the IISc design, [7] is used for treating the water and recirculation [8]. Water used for scrubbing the gas has been treated in both the cases. Table III presents the results for both the cases.

[2]

[3] 4

CONCLUSIONS [4]

The paper presents the use of coconut fronds as a fuel for gasification and compares the performance with woody biomass. The paper provides the performance comparison between these two fuels. The paper also compares the water quality between the two fuels before and after treatment. It has been shown that the low density material and reasonably high ash content fuel can be successfully gasified to meet engine quality gas. 5

[5]

[6]

ACKNOWLEDGEMENTS

The authors wish to acknowledge the support of the Ministry for New and Renewable Energy Sources (MNRE), Government of India, for all the research and development activities at the Institute. 6

[7]

[8]

REFERENCES

[1] S. Dasappa, Biomass gasification: Some of the

experiences from India, Handbook Biomass gasification, Second Edition, BTG, Netherlands, 2012.\Book chapter_Handbook.pdf G.S. Sheshagiri, N.K.S. Rajan, S. Dasappa, P.J. Paul “Agro residue mapping of India”, Proceedings of the 17th European Biomass Conference and Exhibition, 2009, 375-382 http://www.mnre.gov.in/schemes/gridconnected/biomass-powercogen/ viewed on June 10 2014. Department of Agriculture Karshika Keralam. Government of Kerala. India. (n.d.). "Coconut Cultivation". Retrieved 2009-12-06. [4] S. Dasappa, P.J. Paul, H.S. Mukunda, N.K.S. Rajan, G. Sridhar and H.V. Sridhar. Biomass gasification technology – a route to meet energy needs, Current Science, 2004, Vol. 87, No. 7, pp. 908-916. H.S. Mukunda, P.J. Paul, S. Dasappa, U. Shrinivasa, H. Sharan, R. Buehler, H. Kaufmann and P. Hasler, Results of an Indo-Swiss programme for qualification and testing of a 300 kW IISc-Dasag gasifier, Energy for Sustainable Development, 1994, Vol. 1, No. 4, pp. 46-50. S Dasappa, D.N. Subbukrishna, K.C. Suresh, P.J. Paul and G. S. Prabhu, Operational experience on a grid connected 100 kWe biomass gasification power plant in Karnataka, Energy for Sustainable Development, 15, 2011, 231–239, Elsevier. CPCB, Small Scale Industry: Waste Water Discharge Standards, CPCB Notification No. ½(71)/87 plg. dated 7th April 1988

Table III: Water quality for both the fuels after treatment S ump Water Analysis Report before and after test run PARAMETERS

S L. NO

Descrip tion

LIMITS AS PER KS PCB

Coconut fronds

S ubabul wood

Pale yellow coloured liquid having sediments with slight odour

Pale yellow coloured liquid having sediments with slight odour

Before

After

Before

After

1

pH value

6.0 to 9.0

7.67

7.63

7.71

7.63

2

Total Chlorides, as CI, mg/L

M ax. 1000

106.1

144.6

144.6

154

3

Total Dissolved Solids, mg/L

M ax.2100

536

528

508

572

4

Total Suspended Solids, mg/L

M ax.100

80

100

120

190

5

M ax.250

80.6

50.9

127.2

182.3

6

Chemical Oxygen Demand. M g/L Biochemical Oxygen Demand, mg/L (for 3 days at 27 Deg C)

7

Total Kjeldahl Nitrogen, as N, mg/L

8 9

M ax.30

18

10.5

16.5

65

M ax.50

141

145.8

230.9

267.3

Amonical Nitrogen, as N, mg/L

M ax.5.0

127.3

135.7

212

249

Free Ammomia, as NH3, mg/L

M ax.100

2.2

2.4

3.7

4.4

M ax.10