Biomass Pelletization Process

Biomass pellets are a popular type of biomass fuel, generally made from wood wastes, agricultural biomass, commercial grasses and forestry residues. In addition to savings in transportation and storage, pelletization of biomass facilitates easy and cost effective handling. Dense cubes pellets have the flowability characteristics similar to those of cereal grains. The regular geometry and small size of biomass pellets allow automatic feeding with very fine calibration. High density of pellets also permits compact storage and rational transport over long distance. Pellets are extremely dense and can be produced with a low moisture content that allows them to be burned with very high combustion efficiency.

biomass-pellets

Biomass pelletization is a standard method for the production of high density, solid energy carriers from biomass. Pellets are manufactured in several types and grades as fuels for electric power plants, homes, and other applications. Pellet-making equipment is available at a variety of sizes and scales, which allows manufacture at domestic as well industrial-scale production. Pellets have a cylindrical shape and are about 6-25 mm in diameter and 3-50 mm in length. There are European standards for biomass pellets and raw material classification (EN 14961-1, EN 14961-2 and EN 14961-6) and international ISO standards under development (ISO/DIS 17225-1, ISO/DIS 17225-2 and ISO/DIS 17225-6).

Process Description

The biomass pelletization process consists of multiple steps including raw material pre-treatment, pelletization and post-treatment. The first step in the pelletization process is the preparation of feedstock which includes selecting a feedstock suitable for this process, its filtration, storage and protection. Raw materials used are sawdust, wood shavings, wood wastes, agricultural residues like straw, switchgrass etc. Filtration is done to remove unwanted materials like stone, metal, etc. The feedstock should be stored in such a manner that it is away from impurities and moisture. In cases where there are different types of feedstock, a blending process is used to achieve consistency.

The moisture content in biomass can be considerably high and are usually up to 50% – 60% which should be reduced to 10 to 15%. Rotary drum dryer is the most common equipment used for this purpose. Superheated steam dryers, flash dryers, spouted bed dryers and belt dryers can also be used. Drying increases the efficiency of biomass and it produces almost no smoke on combustion. It should be noted that the feedstock should not be over dried, as a small amount of moisture helps in binding the biomass particles. The drying process is the most energy intensive process and accounts for about 70% of the total energy used in the pelletization process.

Schematic of Pelletization of Woody Biomass

Before feeding biomass to pellet mills, the biomass should be reduced to small particles of the order of not more than 3mm. If the pellet size is too large or too small, it affects the quality of pellet and in turn increases the energy consumption. Therefore the particles should have proper size and should be consistent. Size reduction is done by grinding using a hammer mill equipped with a screen of size 3.2 to 6.4 mm. If the feedstock is quite large, it goes through a chipper before grinding.

The next and the most important step is pelletization where biomass is compressed against a heated metal plate (known as die) using a roller. The die consists of holes of fixed diameter through which the biomass passes under high pressure. Due to the high pressure, frictional forces increase, leading to a considerable rise in temperature. High temperature causes the lignin and resins present in biomass to soften which acts as a binding agent between the biomass fibers. This way the biomass particles fuse to form pellets.

The rate of production and electrical energy used in the pelletization of biomass are strongly correlated to the raw material type and processing conditions such as moisture content and feed size. The The average energy required to pelletize biomass is roughly between 16 kWh/t and 49kWh/t. During pelletization, a large fraction of the process energy is used to make the biomass flow into the inlets of the press channels.

Binders or lubricants may be added in some cases to produce higher quality pellets. Binders increase the pellet density and durability. Wood contains natural resins which act as a binder. Similarly, sawdust contains lignin which holds the pellet together. However, agricultural residues do not contain much resins or lignin, and so a stabilizing agent needs to be added in this case. Distillers dry grains or potato starch is some commonly used binders. The use of natural additives depends on biomass composition and the mass proportion between cellulose, hemicelluloses, lignin and inorganics.

Due to the friction generated in the die, excess heat is developed. Thus, the pellets are very soft and hot (about 70 to 90oC). It needs to be cooled and dried before its storage or packaging. The pellets may then be passed through a vibrating screen to remove fine materials. This ensures that the fuel source is clean and dust free.

The pellets are packed into bags using an overhead hopper and a conveyor belt. Pellets are stored in elevated storage bins or ground level silos. The packaging should be such that the pellets are protected from moisture and pollutants. Commercial pellet mills and other pelletizing equipment are widely available across the globe.

Why Businesses Need to Reduce Their Carbon Output?

According to a recent Nielsen study, 81 percent of consumers feel strongly that businesses should be taking measures to reduce their impact on the environment. This passion is shared across generations, and it’s safe to say that businesses that have little regard for their corporate social responsibility are significantly less desirable to consumers.

Despite this, a 2018 survey by Carbon Credentials found that only 10 percent of UK businesses had strategies in place to cut carbon emissions. Of those that did, none had a set science-based target in their carbon reduction plan. We know that climate change will devastate the economy and drastically increase the cost of doing business. That’s not even mentioning how it will impact resource scarcity and the global population as a whole.

At the same time, businesses that take the initiative to reduce their carbon footprint can look forward to many more immediate benefits. Here’s why your business needs to conduct a full carbon audit to reduce its carbon output and do to highlight climate action in the sustainability reports.

Cost Savings

Naturally, your expenses go down with your resource usage. From using more efficient equipment to streamlining your transportation operations to recycling office supplies, there are countless measures every business can take to make this happen. Within the first month, you’ll have more money to allocate towards growth – instead of utility bills.

Regulatory and Tax Compliance

Year-on-year, laws are passed to penalise businesses that don’t make an effort to reduce their impact on the environment and reward those that do. In the UK, this includes the Climate Change Levy, the EU Emissions Trading System and capital allowances on energy-efficient equipment, among other schemes.

Public Image

A 2015 Nielsen study of 30,000 consumers found that 66 percent of them would pay more for sustainably manufactured products. Among millennials, that portion increases to 77 percent. Gen Z is known to be even more conscious in this regard. The more your business cares, the more your customers will care about your business.

Employee Morale

In a similar light, going green fosters positive feelings from your employees as well. This has many benefits. For one, your staff will be more productive and motivated to achieve if they know they’re working for a good cause. Additionally, turnover will be reduced as employees will be less compelled to leave a work community that cares.

The Bigger Picture

This should go without saying, but reducing your company’s environmental impact has lasting benefits for your community and the economy as a whole. The likelihood of your long-term success and prosperity is far greater if the environment is in better shape.

What You Can Do

The list of measures your business can take to become more environmentally conscious is quite frankly endless. Get started by taking a look at this post on Utility Bidder, an energy supplier comparison website, about some simple ways that businesses can reduce their carbon output. The internet serves as a wealth of information on this topic.

Implementing greener practises is extremely beneficial to your business and more often than not, it is a dead-simple process. Getting started today will help you reap the benefits and reach your business goals sooner.