To understand more about refining your selected biomass source, please add the following section(s) to your report

Energy Crop Refining

Rapeseed Oil Production

The main problem in the extraction of rapeseed oil is to achieve a high yield of oil while maintaining high quality of protein. Therefore, operational parameters should be optimized during preliminary operations, processing and isolation of oil. Primary processing includes pre-processing, extraction proper and utilization of by-products.

Pre-treatment-In preparing oilseed for the extraction of its oil, energy must be used to rupture or weaken the walls of the oil-containing cells. This energy is partially mechanical work, which includes; breaking, grinding, rolling, pressing and pelleting. The partially thermal energy to degrade cell walls, reduce oil viscosity and adjust moisture content.

Dehulling-The purpose of dehulling is to remove the major part of the fiber and a group of pigments which, passing into the meal, would lower its feeding value. The overall dehulling process includes: cooking, dehulling itself and separation of the hulls. A cooking period of 10-15 min is usually sufficient, since during this time at 90-97(C the seed reaches moisture content approximately 6%. The dehulling itself takes place in a disc mill, in which the disc spacing and the rotational speed can be varied. Hull separation can be combined with the removal of sulfur compounds.

Rapeseed Oil Extraction – Extraction of oil from flaked rapeseed can proceed by one of the following processes: direct screw pressing, direct solvent extraction, and pre-press solvent extraction. The pre-press solvent extraction process is a classical system of processing rapeseed in which the seed is initially expelled under pressure to release a portion of the available oil; and the residue is than solvent extracted. This method is still used by many oil producing manufacturers, with some modifications, such as pretreatment of rapeseeds described above. Pre-press solvent extraction is probably one of the most economical processes.

A prepress processing steps include:
1. Seed cleaning-
Current rapeseed cleaning equipment typically consists of three basic steps: aspiration, screen separation to remove oversized particles, and screen separation to remove undersized particles. Most equipment can provide all three steps in a single unit.

2. Preconditioning-Preheating the whole seed prior to processing (to about 30-40(C) by indirect heating or direct hot air contact. This process improves flaking, screw pressing capacity, cake formation, extractability, and hexane recovery from the extracted canola flakes.

3. Flaking-In order to extract the oil, cell walls must be ruptured to allow the lipid particles to migrate to the outer surface of the flake. The lipid portion is separated from the solid flake. This allows a solvent to penetrate into cellular structure dissolving and diluting the lipid portions. Next, this lipid portion flows out of the cell structure and onto the outer surface of the flake. The preheated rapeseed is flaked between two smooth surface cast-iron rolls.

4. Cooking-Rapeseed flakes are heated in a stacked cooker (at about 75-85(C).

5. Screw pressing-This step is obtained to remove 60% – 70% of the oil from rapeseed flakes, and to compress the small fragile rapeseed flakes into a more dense and durable cake to facilitate good solvent contact and percolation in the extractor.

6. Solvent extraction-Further extraction of oil seeds and press cake with hexane.

7. Desolventizing-Removal of hexane solvent from the extracted cake.

8. Distillation-Hexane recovery from canola oil.

9. Degumming-Removal of the rapeseed gums, and free moisture, cooling of dry oil and then transfer to the refining process or into a storage.

Oil Purification
Refining-The refining process involves degumming, neutralization, drying, bleaching, and deodorization. Crude oil from extraction has to be refined to obtain a high quality oil. Natural impurities of crude rapeseed oil include water, dirt, phosphatide gums, free fatty acids, colour matter, odiferous and flavorous substances, natural breakdown and oxidation products of the oil itself. There are two methods for refining edible oils: alkali and physical refining.

1. Degumming-Gums compose about 2% of solvent-extracted rapeseed oil. Degumming treatment commonly uses hot water or steam plus phosphoric acid, citric acid, or other acidic materials. Precipitated gums are removed by continuous centrifugation.

2. Neutralization-Free fatty acids due to the enzymatic breakdown of oil, can be neutralized with alkali solution. After the alkali treatment the oil is washed with hot water to remove traces of soaps that can reduce stability of oil. In addition, pigments of oil, such as chlorophyll, also undergo partial decomposition during neutralization.

3. Drying-The purpose of drying is to remove traces of water from the oil, which improves stability and frying performance.

4. Bleaching-A common method of bleaching is by adsorption of the color producing substances on an adsorbent material. Bentonite (or acid-activated earth clay) and Fuller’s earth have been used most extensively for bleaching rapeseed oils. Rapeseed oil contains large amounts of chlorophylloid pigments that undergo autooxidation, it is more difficult to bleach rapeseed oil than other vegetable oils. However, during refining, degumming removes approximately 38% of chlorophyll b, neutralization removes mainly chlorophyll a, and deodorizing removes carotenes. Overall refining carried out on laboratory scale removes 95.5% of carotene and approximately 85% of chlorophylls.

Pyrolysis Oil

Pyrolysis or dry distillation is process where wood, or other biomass that includes carbon, is heated to a high temperature without oxygen in order to make the biomass decompose into different fractions. Typically the final product conducts carbon, different tars, fenols and acids. The common name for liquid fuel produced by pyrolysis process is pyrolysis oil. Pyrolysis oil is flammable liquid with a complex chemical composition. Pyrolysis oil can be used for replacing fossil fuels and as a raw material in different chemical processes. The pyrolysis process can be modified and adjusted by changing the reaction pressure, temperature and time. All these adjustments affect properties of the final product.

In slow pyrolysis production, different final products can be separated from one same raw material by staggering processes. The most traditional slow pyrolysis process is making tar or wood coal in a clamp (charcoal kiln). Wood is heated in closed system or chamber without air entering the process, and so there is an absence of oxygen. When wood is heated but not combusted, different gases are released from wood and they can be separated. These gases can be turned into liquid by cooling. Separation is based on the knowledge that different gases evaporate from the wood at different temperatures. By adjusting the temperature, pressure and reaction time and cooling of the gases at the end, different liquid fuels can be collected.

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Different adjustments to pyrolysis oil productionprocess results in different kinds of pyrolysis oil.

 

The pyrolysis process can be described in following way:

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In slow pyrolysis the final product has, in relation to the raw material dry material proportion, in average 30 % of Carbon and 50% of pyrolysis oil. The rest of the product is incondensable gases which can be combusted and use as a heat for the process or drying the raw material. The carbon in process can be used as a fuel, change to activated carbon or to refine in other industry processes. Carbon can be stored to soil as such it is coming from the process. In agricultural land carbon is improving the water and nutrient balance, especially in soil which has fewer nutrients. This terra-preta method has been used in South-America over thousand years. This method is also called agro carbon pyrolysis and the product coming from pyrolysis can be helping to solve two big challenges in earth: storing carbon and increase the potential to produce more food for growing population of human.

Fast pyrolysis is, as the name says, really fast process which is over in only couple of seconds. Fast pyrolysis can be made really efficient in an industrial application and also acquisition is better than in slow pyrolysis process. Fast pyrolysis is nearly only used to make pyrolysis oil. One of the examples is in November 2013 opened pyrolysis oil plant in Joensuu. The plant is integrated to existing CHP plant that is taken care of the district heating of Joensuu. In Joensuu delimbed stem wood is grinted and dried to 10 % moisture content. This wood dust is mixed in own reactor with sand and gas stream that is separated from the 800 Celsius degree fluiside bed boiler. The wood dust is changed in a couple of seconds to gas and carbon. After that gas is separated from sand-carbon mixture in own separator and gas is cooled to liquid. The carbon is used for the CHP boiler and is combusted there together with other fuel

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Pyrolysis reaction of Fortum’s power plant in Joensuu. Picture made by Fortum and from source: http://www.fortum.com/SiteCollectionDocuments/Media/Fortum_App2_illustration_integrated_pyrolysis_reactor.pdf

Pyrolysis oil is used to replace heavy fuel oil in energy production. Pyrolysis oil is acidic and the chemical properties slowly change during storage. The use of pyrolysis oil in old boilers is quite straight forward and when used for energy production, it is already economically reasonable to have it in market. There is also the possibility of refining the product more and to make bio diesel or petrol from it. Many industries are interested in the thousands of different components that pyrolysis oil has which could be used in medicine, coating and nourishment/food. Smoke aromas and micro oven food browning chemicals are normally refined from pyrolysis oil.

Table.Differences Between Pyrolysis oil and heavy fuel oil properties

Properties

Pyrolysis Oil

Heavy fuel oil

Water content

15-30

0,1

pH

2,5

Density

1,2

0,94

Ash

0-0,2

0,1

Heat caloric value (MJ/kg)

16-19

40

Element concentration, %
Carbon (C)

54-58

85

Hydrogen (H)

5,5-7,0

11

Oxygen (O)

35-40

1,0

Nitrogen (N)

0-0,2

0,3

 

Briquettes

Material for briquettes can be sawdust, energy crop straw, wood branches, rice hull, etc. Before briquetting, the raw materials need to be prepared for the briquette process. The process starts from grinding the raw material using a hammer mill. Hammer mills are suitable for crushing different kinds of straw or wood log with diameter size of less than 200mm. After the raw material is milled, the output diameter can be around 3-5mm, which is suitable for further briquetting.

Next the grinded raw materials need to dry. Different saw dust dryers can be used like belt dryer or drum dryer. Drying is necessary as the moisture content is usually high, perhaps more than 12% in raw material at this point of process, and too high for the continuing briquette process.

The next step is briquetting which is the major process. The basic principle of the briquetting machine is to compress the raw materials at high temperature and then press the material into a square outside with an empty middle, and a high density or prismatic briquette. Temperature does not need to be as high as in pellet production but the moisture content needs to reach 8%-12%. If the moisture content is high, the briquette may scatter; but if the moisture is too low, the briquette may have cracks. Wood briquettes can be also refined into charcoal by carbonisation. (http://www.charcoalbriquettemachine.com/Application/how-to-make-charcoal-briquettes.html)

Pellets

Refining_pellet1

Woodpellet production starts with receiveing raw material. Usually raw materials, like sawdust from different tree species, are kept separate, because the pellet pressing process is very sensitive tor raw material properties. After the arrival the raw material is dried (if not already dry) down to 8-15% moisture content. Drying is done in belt dryers or drum dryers. After drying, raw material is grinded to fine, evenly sized dust (15-5 mm) by hammer mills or knife mills. Milled wood dust is carefully fed to a pellet press, where dust is pressed through 40-70mm long and 6-12 mm wide channels of ‘die’. Friction and high pressure heats wood dust to over 60 centigrade, usually up to 100-130, when lignin comes out of the wood and acts like a glue. Lignin attaches the raw material particles together and when pellets cool down in the cooler, they form hard and solid granules with high density.

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Production of pellets, pictures taken by Lauri Sikanen, Metla

After cooling pellets will are stored in silos and transported to customers by trucks, trains or tanker ships.

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Photo taken by Robert Prinz, Metla

Wood Refining

Refining means that the wood biomass is converted to form that it is easier to transport, store and combust/convert to energy. The most common refining methods are pelletising, pressing to briquettes or changing woody biomass to different wood oil such as pyrolysis oil.

wood-refining

Depending on your earlier choices when processing BISCUIT, you will have a more detailed report of different wood refining process of your interest.