Wheat and wood – a perfect bind
The use of binders such as starch in pelleting as a means to improve pellet durability has both its supporters and those that think it unnecessary.
"It is not simply a binder, it is a tailor-made wheat starch derived technical performance enhancer in which improved binding is one benefit," remarked Bo Jönsson from Germany-based consultancy company COMASA GmbH when we met to discuss the merits of binders at a pellet conference in Sweden.
It turned out to be quite the learning experience. Wheat is one of the oldest grains known to mankind, and it is also the sole passion for the fifth-generation family owned and managed Crespel & Deiters Group in Ibbenbüren, Germany. To say that the company knows a thing or two about the grain and what it can be used for is an understatement – the company celebrates 160 years in business this year.
Crespel & Deiters Group processes over 320 000 tonnes of wheat per annum for a wide range of derived products for the food and feed industries as well as for industrial applications including binders for the wood pellet industry, which are provided by the corporate division C&D Technical Applications.
The corporate division C&D Corrugating & Paper is well known as one of leading specialists in Europe for wheat starch-based adhesive solutions that support the corrugated board industry in the cost-efficient manufacture of high-quality corrugated board.
Technical performance enhancer
The use of binders such as starch in wood pelleting has both its supporters and those that think it unnecessary. In Germany and Austria for instance, the use of binders as a means to improve pellet durability and colour is commonplace amongst pellet producers whereas, in other regions, it is not.
Jönsson, who is assisting C&D Technical Applications with introducing its wheat starch additive to the Nordic wood pellet industry, pointed out that, to start with, there are “considerable differences between starch and starch” depending on the source, type and how it has been processed – potato starch from France, cassava starch from Thailand, corn (maize) starch from the United States or rice starch from India.
The former two are tubers that grow underground whereas the latter two are grains that grow above ground to illustrate an obvious difference.
It is a fair point, though, as with any technical performance-enhancing additive that is consumed in a process, the challenge is to make the benefit(s) visible and ascribe a tangible monetary value to said benefit(s). In an ideal world, if the value of the benefit(s) outweighs the cost of its consumption, then the decision seems straightforward enough.
Properties of wheat starch
Before diving into the benefits, Carsten Mergelmeyer, Corporate Development Manager at C&D Technical Applications gave some background into what the company actually does. He explained that each constituent part of the wheat grain; the seed coat or bran, aleurone layer, endosperm, and germ, has its own properties and that all the constituents are used.
Around 15 percent of the company’s products are used in the food industry with the remaining 85 percent used in the pet-food, animal feed, and non-food industrial applications.
The grain is first ground and then the endosperm is broken down into its components through the addition of fresh water and application of heat. This mixture is then sieved and centrifuged to obtain four main base products; the wheat starches, proteins, fibres, and extracts.
These four base products along with the bran are then refined in further processing steps such as mixing, extrusion, thermal and chemical modification into various functional product categories, each of which that can be specially tailored for customer end-uses in the food, feed, and non-food industries.
One of these product categories is pre-gelatinised wheat starch and it is this category that is used as a performance improvement additive within the wood pellet industry.
Wheat starch forms a highly stable gel with strong adhesive features and it is this basic characteristic that is exploited for enhanced wood pellet production, said Carsten Mergelmeyer.
Improving process efficiency and pellet quality
The wheat starch additive is dosed as a powder into the mixer prior the pellet press and gelatinises on contact with moisture.
The pre-gelatinisation process enables each powder particle to instantaneously gelatinise on contact with water, without clumping, said Jönsson, pre-empting a home-baking experience related follow-on question.
Mergelmeyer explained that these micro-gel particles have a lubricating and temperature reducing effect on the pelleting process. This translates into lower pellet press temperatures, longer and more stable run times for the die as a result of less friction.
Combined these add up to less pellet press power consumption and lower operations and maintenance (O&M) costs per tonne pellets produced. Or if one prefers, more pellets produced per unit of energy used.
The pellets have improved durability thanks to the adhesive property which means less dust and fines in post-press pellet handling and a lighter colour, which for some pellet markets, is an important aesthetical attribute.
Do the benefits add up?
According to Jönsson, up to 15 percent reduction of pellet press power consumption can be achieved with CRESPOTEC-Additives from C&D Technical Applications, applied between 0.3 and 1.5 percent by weight.
It’s not simply a question of applying an arbitrary dose of starch to achieve such energy efficiency gains and overdosing just costs money. The percentage of starch needed for optimum results varies for each plant and is dependent on a number of factors such as wood species mix, particle size, pellet press type and brand to mention a few, Jönsson stressed.
Both Jönsson and Mergelmeyer emphasized that establishing the pellet press baseline performance and pellet quality is critical, as it is against this that the benefit of adding starch is benchmarked. The next obstacle is site-specific – installing a dosing unit and storage space for the additive that comes in big bags and needs to be kept dry.
For each client, we run tests to find the optimum dosing level and application point. Usually, this is followed by a trial over a period of time so that the additive’s performance can be compared to the baseline benchmark and the benefits calculated. These trials are supported by COMASA (application consultancy), MAFA (technical equipment) and C&D Technical Applications (development & production of functional binding agents) in a close partnership. By then we should have proved our case and it becomes an informed decision that rests with the client, ended Carsten Mergelmeyer.
This article was first published in Pellets Special 4 2018. Note that as a magazine subscriber you get access to the e-magazine and articles like this before the print edition reaches your desk!