4.1 Biomass Gasification to Replace Oil in Rubber Sector

4.1 Biomass gasification to replace oil in rubber sector

S. Dasappa*, P J Paul and G. AmarKumar+

Centre for Sustainable technologies

Combustion, Gasification, Propulsion Laboratory (CGPL),

Indian Institute of Science, Bangalore: 560 012, India

Ph: +918023600536 ; Fax: +918023601692

, ,

+Bioresidue Energy Technology Pvt. Ltd

Bangalore; India

Abstract

ABSTRACTCrumb rubber as a product is being used rubber industry. Large number of rubber industries accepts the dried granules of 3 – 8 mm material for further processing. Hot air is generally generated using fossil fuel, both diesel or kerosene burners and diluting the flue gas to 120 C.

The twin air entry, re-burn biomass gasification system of IISc has resulted in developing package for low temperature drier application. The technology package involves generating clean producer gas to be burnt in producer gas burners with right dilution to ensure a flue gas at 120 C or in a thermic fluid heater to replace oil. The technological challenge has been to provide a cost effective solution for safe and efficient operation of the drier to replace oil. Typical fuel consumption depending upon the capacity of the plant is about 20 –50 lts per hour, being replaced by a gasification system of about 80 to 200 kg/hr.

The continuous tray drier with a residence of 2 hours are in the capacity output of 500 to 1000 kg/hr. Over 50,000 hours of operation at one location has indicated that a fuel replacement of 3.25 kg of biomass per kg of fossil fuel. These systems are operated on 24 hours basis and operates for about 6000 – 7000 annually. A total of 12 systems in different industries with a total drier capacity of about 12 tons per hour, amounting to annual capacity of 72,000 tons have been replaced by gasification systems of about2 ton per hour capacity.The technology package is ideally suited for the CDM programs.

Key words : gasification, rubber drying, thermic fluid heaters, producer gas

Introduction

About 8-10 million tons of natural rubber is produced and Asia is the main source of natural rubber, accounting for around 94%. India is the fourth largest rubber producers in the world. The three largest natural rubber producing countries (Indonesia, Malaysia and Thailand) together account for around 72% of all production. India produces 0.86 million tons of natural rubber used in various applications. In India rubber is predominantly a small holders’ crop and over 87% of the rubber is from this sector.

Dry natural rubber graded or the basis of technical parameters are called Technically Specified Rubbers. The International standards Organisation (ISO) first came out with the draft Technical Specifications for Natural Rubber during 1964. Based on these specifications, Malaysia introduced their Standard Malaysian Rubber (SMR) in 1965 and since then all the Natural Rubber producing countries started producing and marketing NR as Technically Specified Rubbers. The TSR's are mostly the block types made adopting new methods of processing. The blocks are generally 33 1/3kg bales in the International market and 25kg in India. All the block rubbers are also guaranteed to conform to certain technical specifications as laid out by the national schemes or by the ISO_2000 standard.

The share of TSR in the export market of NR accounts a little over 60%. Also in the international market, TSR's are the major volume grades of dry rubber in production and exports in the major NR exporting countries of the world.

The advantages claimed for the Technically Specified Rubbers over the conventional sheet and crepe grades of rubbers are the following:

• Being available in a limited number of well defined grades, correct choice of grades according to requirements by the consumers, is rather easy.
• Being possible to assess the actual content of foreign and volatile matter, mistakes can be avoided in deciding the actual worth of the material.
• Being marketed as compact, polythene wrapped bales, degradation of the rubber on storage, handling and transportation can be prevented
• Being in standard size and compact, considerable savings can be made in transport through mechanised handling and containerization

From a consideration of all the above, it can be noted that Technically Specified Natural Rubbers are well known as the modern form of Natural Rubber, designed mainly.

• To meet the requirements of the rubber consumers better,
• To ensure value for the money of paid by the consumers and
• To ensure, better uniformity and consistency in the quality of NR.

Uses

Can be used for high quality products such as mechanical mountings for engine and machinery, railway buffers, bridge bearings, vehicle suspension systems and general automotive components large truck tyre tread, conveyor belt covers, cushion gum for retreading, wind-shield wiper blades, masking tapes, brake assembly units, injection moulded products including rubber/metal bonded components, low density sponge, tee gum cushion compounds, springs, industrial rolls, inner tubes and cement.

There are over45 numbersof industries involved in the processing of crumb rubber in the states of the Kerala, Karnataka and Tamil Nadu in Southern India.Manufacturers of Technically specified Rubber (TSR), also called as crumb rubber. Large numbers of industries supply the processed rubber to leading tyre manufacturers in the country.

Typical the processes involved in the raw material to the final form are

• Stages of soaking, squeezing and shredding.
• Drying with moisture reduction from 35% to <1%.
• Hydraulic pressing to final form.

Crumb rubber as a product is being used by rubber industry. Large number of rubber industries accepts the dried granules of 3 – 8 mm material for further processing. The drying is an important process carried out at the plantations to reduce the moisture content. Drying is practised in continuous tray dryers using hot air at 120 C. Hot air is generally generated using fossil fuel, both diesel or kerosene burners and diluting the flue gas to 120 C. Typical fuel consumption is about 35 litres per ton of crumb rubber.

Figure .. provides the details of the typical drying system. It consists of the burner and dilution air to ensure hot air/gas temperature at the dryer inlet at 120 C. The hot air/gas travel past the trolleys filled with material to be dried. Typical residence time for the trolleys in the dryer is about 120 mins. The moist laden gases exit at the end of the tunnel. The plants operate on a 24 hour basis during season and on an average about 16 hours during other period.

Drying is carried out in two modes, direct drying, where the flue gases of the product of combustion come in contact with the raw material and indirect, where a medium is heated, which is further utilised in the drying process. Drying is carried out in using continuous trolley type tunnel dryer, accommodating trolleys of about one m3 volume in each. Typical fuel consumption in a direct drying is about 35 Litres of fuel per ton of crumb rubber. Diesel or super kerosene oil is being used as fuel in this sector and the hot air/gas temperature to the drier is 1200C. Typical efficiencies of these dryer are in the range of 60 to 65 %.

The present paper discusses the work carried out on using biomass gasification with multi-fuel capability to replace oil in the driers. Adaptation of the IISc biomass gasification technology to meet the energy needs of the crumb rubber drier through specially designed burners to use producer gas for retrofitting the existing driers. Woody biomass and coconut shells fairly make a large percentage of biomass available in southern part of India and are used as the fuel to replace the oil in these driers.

The intervention

Drying using of diesel or super kerosene oil had a significant cost on the process. The contribution of diesel cost was about 14 USD per ton of dried rubber (@0.38 USD per litre and 1USD = 48 INR – 2002 prices). Drive to replace the oil by other alternative was reviewed by the industries. Biomass gasification was found to be one such process that provided the necessary economic benefits.

The gasification system

The gasification system consisted of an open top dual air entry system, with multi-fuel capability. The system comprised of reactor, a cyclone to remove dry dust and scrubbers to cool and clean the gas. Details about the gasification system is as in (dasappa et al … ). Typical gas composition is CO ~ 20 %, H2 ~ 20 %, CH4 ~ 1.5 %, CO2 ~ 12 % and rest N2 with an average calorific value of about 4.7±0.2 MJ/kg. The gas is drawn into a specially designed twin lobe swirl burner lined with ceramic. Necessary dilution is carried out to achieve the dryer temperature.

Gasification system for a 225 kW th direct drier

The drier rated of about 22 lts per hour of fossil, was substituted using a 80 kg/hr gasification system. The fuel used was coconut shells as it is available in abundance. Coconut shells have less than 1 % ash, particle density ~ 1000 kg/m3 and with bulk density of sized in the range of 400 – 500 kg/m3. The fuel preparation is limited to crushing the half shells to 2 to 3 pieces.

The gasification system was installed in the year 2002 at this location. Table 1 summarizes the operations for the first year after installation. The gasification system was operated for over 4500 hours during the first year, which is close to about 95 % of the factory operation time. This operation instilled confidence in the rubber sector. From Table 1 it is clear that 1 lts of oil has been replaced by about 3.25 kg of biomass.

Table 1 : Initial operations at Ideal Crumb rubber factory

Month / Hours of operation / Biomass consumed, kg / Diesel saved lits
Jul-02 / 316 / 25057 / 6952
Aug-02 / 350 / 24500 / 7700
Sep-02 / 491 / 35644 / 10802
Oct-02 / 502 / 36968 / 11044
Nov-02 / 234 / 18220 / 5148
Dec-02 / 401 / 26658 / 8822
Jan-03 / 418 / 27974 / 9196
Feb-03 / 416 / 29249 / 9152
Mar-03 / 432 / 30691 / 9504
Apr-03 / 312 / 22512 / 6864
May-03 / 281 / 20100 / 6182
Jun-03 / 502 / 36529 / 11044
Total / 4655 / 334102 / 102410

An energy balance suggests that the with a gasification efficiency of 75 %, the thermal energy input to the drier is estimated at 840 kW compared with oil at 790 kW. Based on this it is evident that the overall thermal efficiency of the fossil fuel based system is achieved using the gasification system.

Over the last 7 years the system has operated for over 50,000 hours, amounting to an average 6500 hours in an year. Apart from coconut shells as the fuel, the industry has used saw dust briquettes, cashew nut shell and wood chips, depending upon the availability. During this period, the overall economics has been extremely favorable to the industry. Further the industry has found that cost of drying has reduced to less than half compared to the diesel fuel operation.

Experience suggests that gasification system can be operated for over 1200 hours non-stop. Over a period of 7 years, 6 maintenances have been carried out on an yearly basis. This ensures continuous operability.

Gasification system for a 1.25 MkW th indirect drier

Use of gasification system to replace oil in a thermic fluid heater in the indirect drier, where heat exchange with the fluid and air is carried out. This application provides the client to have better quality rubber, sans contact with the flue gases.

The process requires, a high and low (Continuous modulation of) gas flow rate into the combustion chamber of the thermic fluid heater in order to maintain the temperature of the fluid medium. This has been achieved using gas regulation as soon as the fluid temperature is attained.

The schematic diagram provided in Figure… details the process.

Figure … Schematic of the indirect drier

The gasification system

About 160 kg/hr gasification system has been installed in an industrial outfit of Rubber board to replace the about 40 lts of oil in the thermic fluid heating system. This system was slightly over designed for some inefficiency in the indirect process.

The system was installed during 2007 and has operated for over 10,000 hours. An average fuel consumption of about 130 kg for a drier output of about 1 ton per hour. Average daily consumption of biomass was in the range of 2.9 tons, with an average 600 hours monthly.

The gasification system is similar to the earlier system, except that the gas burner was to accomdated on the existing thermopac retaining the oil burner.

The operations were designed to incorporate PID controller to maintain the gas flow rate as per the requirement of the thermopac. a motorised valve along with a PID controller with the feedback from the thermocouple on the thermic fluid line acts to regulate the gas flow.

Thermocouples have been used to detect flame failure and divert the gas towards flare to ensure safety. Manually controlled valves are provided to override the control loop in case of an emergency. While maintaining the thermic fluid tempeature at 280 C, depending upon the load, the biomass consumption varies from 90 kg/hr to about 140 kg/hr.

As a part of safe operation, oxygen level in the gas is monitored continously to ensure no premixed gas is in the line. The thermocouples in the flame zone performn the function of flame detection.

The total operation of the plant is inexcess of 10,000. Operational data for the year 2008 is presented in Figure … On an average , the plant has operated for over 300 hours in a month, typical 12 – 15 hours a day and the plant has operated for over 4700 hours replacing about 100,000 kg of oil.

Figure : Operational details performance of the 1.25 MW plant

Figure .. details the biomass consumption and oil replaced during the 12 month period. About 350 tons of biomass has been consumed to replace about 100 tons of oil, amounting to about 3.5 kg of biomass to replace 1 kg of oil. During this period the biomass consumption has been in the range of 60 to 140 kg/hr depending upon the load.

Figure: Oil saved and biomass consumption for the year 2008

A simple energy balance indicates that overall efficiency of biomass to drier product is about 40 %. This includes the efficinceis are device level like, gasification, thermic fluid heater and the drier.

The major outcome of this technology package has been;

• A green energy technology to replace fossil fuel for low temperature application
• Replacement of oil thermic fluid heater
• Specific biomass consumption has been about 8.8 kg dried output / kg of biomass
• A total savings of 2.5 million litre of fossil fuel annually
• Overall economics of operation are the motivating factor for this adaptation

Summary of the performance

Based on the performance of these plants there has been over 12 plants in this sector with a cumulative operation of about 0.2 million hours.The gasification capacity ranges from 50 kg/hr to about 200 kg/hr. These systems are operated on 24 hours basis and operates for about 6000 – 7000 annually. A total of 12 systems in different industries with a total drier capacity of about 12 tons per hour, amounting to annual capacity of 72,000 tons have been replaced by gasification systems of about 1 ton per hour capacity. The amount of fossil fuel saved annually amounts to about 1.6 million litres.

The annual CO2mitigation potential is about4000 tons.

Conclusions

References.