Thermal Conversion Plants for Manufacturing
of Fluid Fuels from Plant Biomass AND ORGANIC WASTES

Conversion plants are designed within the new energy supply and environment protection concept based on the use of local renewable energy sources and bio-fuels. Plant biomass, mainly in the form of agricultural and wood processing wastes, is one of these energy sources.

The major application of biofuels produced by thermal conversion is cogeneration of heat and power (CHP) using diesel engine and gas turbine based on electric power plants and boilers in the range of 10 kW to 100 MW.

Production of gaseous and liquid phase bio-fuels by fast pyrolysis is one of the most demanded thermal conversion technologies insuring maximum use of  not only plant biomass but also low-calorie fossil fuels (lignite, shale fuels, peat coal, vat residue, etc.), municipal organic wastes, agricultural and wood wastes, as well as dedicated biomass produced by sort rotation coppices (SRC) technique.

Fast pyrolysis is the process of organic matter decomposition by high-rate heating to achieve a temperature at which the yield of desired products is maximal. The optimal temperature is determined by the upper condensed-phase limit for particular organic components.

The technological parameters of fast pyrolysis process, as well as the composition and quantity of manufactured products, shall be specified prior to design and dimensioning of  conversion plants for particular kinds of solid or liquid feedstock.

The high-rate heating provides minimum energy dissipation into the environment and maximum decomposition of organic materials followed by vaporisation of the products. The heating time shall be as short as possible to prevent possible undesirable changes of chemical composition and structure of a processed material. The output of a fluid (liquid and gaseous) fuel is determined by the organic fraction content and is, normally, not less than 50%.

The solid fraction is composed of non-organic compounds (ash) and thermally stable organic products such as char and cross-linked polymers. The yield of char, which is usually less compared with other biomass thermal conversion methods, is mainly determined by the share of lignin in the feedstock being processed.

High temperature vaporous products of the thermal decomposition are fed to a condenser to form the so-called bio-oil (i.e. the liquid product fraction). It is a combustible product having substantially (about 20%) higher specific heating value than that of the feedstock it is made of. The other part of the decomposed and vaporised organic matter, which is non-condensable at temperatures close to normal conditions, constitutes the gaseous fuel fraction composed of non-organic (mainly, carbon oxides and water) and low-molecular organic compounds, such as methane, ethane, etc. This fuel fraction can be combusted in the pyrolysis reactor or/and utilised as a motor fuel of diesel engines operating in the gas-and-diesel mode. Fluid fractions of plant biomass pyrolysis products are applicable as an environmentally safe substitution for conventional boiler fuels (black oil and natural gas). Blending into motor fuels is one of the other promising commercial applications of bio-oil today.

In pyrolysis conversion reactors, plant biomass can be heated either by electric heaters or/and burners fuelled with a part of products (liquid or/and gaseous) that the conversion plant generates itself. Typical energy consumption of the conversion plant is 5% to 10% of the total calorific power of the fuels produced. (In fact, it is nearly proportional to the moisture content of a feedstock.)

 

 

The major features of the process are:

—                     high conversion ratio of organic feedstocks,

—                     compact reactor design,

—                     low energy loss,

—                     relatively low cost of heat and power generated from plant biomass pyrolysis products.

In the All-Russian Research Institute for Electrification in Agriculture (VIESH), a pilot conversion plant for manufacturing of fluid fuels from wood sawdust and other plant wastes has been developed in the frame of the contract from the RF Ministry of Power. The plant is designed to produce more than 500 kg/day of fluid fuels (both liquid and gaseous).

Following are the block diagram of technological process and the layout of the plant, along with a short description of the technological process.

 

Block Diagram of Technological Process

Wood sawdust or other crushed organic material, separated from possible extraneous objects, is fed into reactor comprising two stages of thermal conversion. In the first stage section, moisture is extracted from the plant biomass feedstock. The latter is then directed to the pyrolysis stage where it is decomposed to mainly vaporous products. A part of the decomposition products (char) that can not be vaporised within the operating temperature range is taken out of the reactor and is collected in a storage bin. In the separator, the vaporised products of thermal decomposition are purified of solid micro-particles, and in the condenser, they are cooled to form the liquid fuel fraction bio-oil. The non-condensable fraction, pyrolysis gas, is fed to a diesel engine set operating in gas-and-diesel mode to generate electric power, while the liquid fraction is collected in the bio-oil tank.

Bio-oil can be used as boiler fuel or blended into conventional diesel fuel fed to the diesel engine. This fuel blend is, normally, comprises about 5% of bio-oil but its share can be increased up to 15%, if necessary. Hot water vapour and heat energy produced as a result of the thermochemical process is utilised in heat exchangers for local heating and hot water supply.

The pilot plant manufactured at the (VIESH) has been tested with different kinds of feedstock, such as wood chips, wood sawdust, peat coal, lignite, rice husks, wastes of coffee extraction, etc. Following is the typical product distribution for wood sawdust pyrolysis process carried out at medium temperatures of 450 C to 550 C:

 

 

 

 

Layout of pyrolysis plant for liquid and gaseous fuels production and 30 kW dieselgenerator set.	Testing of equipment for biomass conversion info liquid and fuel. Capacity 1 t/day

 

Physicochemical properties of the products:

Physicochemical properties of liquid fraction make it applicable as oven fuel. It is also can be modified or/and blended into conventional oil-derived products to form motor fuels.

Non-condensable gas formed by low-molecular products (up to 30% methane, ethane, propane, hydrogen, carbon oxides) can be effectively applied as either a furnace fuel or motor fuel for internal combustion engines for heat and power co-generation.

Pyrolysis chars physicochemical properties are similar to those of conventional char traditionally used not only for as fuel but also in medicine, steel industry, etc.

One ton of wood sawdust yields about 500 kg of liquid and gaseous fuels.

The payback period of the plant is 3 years.

VIESH is ready to enter into contracts to supply plant biomass pyrolysis plants having a performance rate of 1 ton to 2 tons of feedstock a day. Delivery time is from 6 to 8 months.

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