Organic fertilizer dryer: overcoming quality issues

To feed an ever-growing world population, agricultural businesses strive to maximize crop yield. One way to achieve this is by using fertilizers. Dry fertilizers, especially, dissolve slowly into the soil, making them highly efficient for use in large fields. However, if organic fertilizer dryers are not applied properly, a number of issues may occur. How to prevent them?

Fertilizers definitions

Before we dive into the organic fertilizer production process, let’s get our definitions straight.

Synthetic and organic fertilizers

Roughly speaking, there are two types of fertilizers: inorganic and organic ones. Inorganic, or synthetic fertilizers, are made of synthesized chemicals. They may be ‘straight,’ containing one nutrient, or multi-nutritious, such as NPK fertilizers. The latter contain chemically produced nitrogen, phosphorous, and potassium.
Alternatively, fertilizers made from animal or plant sources are called organic, or natural. Fertilizer from animal waste can consist of manure, but also of bone or blood meal, hides, hoofs, and horns. Peat is the most widely used plant-based fertilizer, but there can be many other plant waste sources.

Over the last years, consumers’ concerns about their health and the environment have led to an increased focus on organically produced foods. As a result, the global market for natural fertilizers is mirroring the growth in organic foods. That’s why in this article, we will zoom in on these fertilizers.

The global organic fertilizer market is steadily growing. Source:

Liquid and dry organic fertilizers

Organic fertilizers are applied in liquid or dry form. Both work well, but there are differences. For instance, liquid organic fertilizer can be easily blended into optimal nutrient levels, or with crop protection products. Furthermore, its content is the same in every drop, making it highly reliable. Liquid fertilizer is also easily applied, both by foliar and ground application.

On the other hand, dry fertilizer releases its nutrients slowly, rendering multiple applications superfluous. This is highly effective, especially when large areas need to be covered. Moreover, dry fertilizer contains not just nutrients, but also organic matter, which helps to improve soil structure and fertility. As both the composition and the nutrient release of natural fertilizers vary, their quality is vital to ensure high crop yield. However, it should not be pursued at the expense of handling characteristics or energy consumption. By optimizing the production process, the fertilizer nutrients can be maintained while preventing handling and processing issues. To zoom in further, in this white paper, we will focus on the production of dry organic fertilizer.

Organic fertilizer production process

Generally speaking, the organic fertilizer production process includes the following steps:

Pretreatment of raw materials

Whether the fertilizer is made from animal waste or plant residue, it is shredded into uniform particles to accelerate compost time.

Windrow composting

Composting can be achieved by using the windrow method: the shredded waste is placed in piles on the ground and regularly turned. While drying, the temperature can reach 55°C. In about four to six weeks, the compost matures.

Grinding and screening

However, the fertilizer is still very wet and coarse. Therefore, it is ground and screened for rocks and debris.

Drying and finish

The next step in the organic fertilizer production process is the drying and optional pelletizing of the compost. There are many ways to go about. At Ventilex, we prefer to use a fluid bed organic fertilizer dryer. In this fertilizer drying machine, a continuous flow of wet granular fertilizer is dried by blowing hot air through the product. The velocity of the air lifts the product, mimicking a liquid state. The direct contact between the natural fertilizer and the hot air maximizes the heat transfer from the drying air to the product, making this one of the most efficient drying processes.

When the drying process is finished, the fertilizer needs to cool down. We achieve this by applying the same principle as above: we blow ambient air or conditioned (cooled) air through the fluidized product. After cooling, an additional step can be applied, using a fertilizer pelletizer to form easy-to-handle pellets. However, this is not mandatory.

Issues with drying fertilizer

At the beginning of this article, we indicated that the improper use of a fertilizer drying machine could lead to several issues.

Caking of fertilizer

One of these potential issues is caking, or lumping, of the fertilizer. This may happen when the product is not dry enough, causing it to agglomerate. Ironically, caking of fertilizer can also happen when the product is dried at overly high temperatures. As a result, the product will continue to dry after it is bagged, which leads to an increase in the humidity of the air surrounding the granules. This, in turn, leads to moisture at the interface between the granules, and, subsequently, caking of the fertilizer.

Product degradation due to overdrying

Another issue has to do with quality. For one, over-drying may lead to deterioration of the nutrients. The trick is to find the optimal temperature for drying without causing damage. After all, organic fertilizers tend to be less nutritious than synthetic ones, so it is of vital importance to maintain the quality of the nutrients.

Product degradation due to rough processing conditions

A third issue has to do with processing conditions. High-frequency fluid bed designs can generate as much as eight gravities of force. This may lead to a breakdown of the product, and, subsequently, to more waste and lower market value.

Fertilizer production – high energy consumption

Fertilizer production is notorious for its high energy consumption. Not only is this environmentally harmful – a feat that should not be associated with anything organic. It also leads to significantly higher operational costs and low margins.

Fertilizer production can lead to extra maintenance and downtime

By its very nature, natural fertilizer is a coarse product. As a result, an organic fertilizer dryer needs to be extremely sturdy to withstand the forces to which it is subjected. If not, it will require a lot of maintenance, repairs, and even replacements, which leads to increased costs and more downtime, and, subsequently, to lower production and profits.

Fertilizer production produces ammonia odors

Organic fertilizer creates nasty odors. The digestate, as well as odor components like volatile fatty acids, emanate ammonia (NH3). Although this is not just a part of fertilizer drying but rather of the total production process, clients mention the odor nuisance regularly, which led us to believe this is a common problem of fertilizer production.

How to overcome these issues?

Whether you are looking for a cow dung drying machine, a chicken manure dryer, or another fertilizer drying machine, it pays off to look into these issues and optimize accordingly. At Ventilex, this is how we tackle the drying problems we mentioned above:

Prevent caking of fertilizer

First of all, our fertilizer drying machine utilizes a gentle reciprocating motion to help fluidize the material. This motion greatly reduces the formation of lumps in the product, thus ensuring a higher quality finished product. Furthermore, the state-of-the-art PLC system offers advanced temperature and humidity control, preventing in-bag humidity accumulation and subsequent caking of fertilizer.

Prevent product degradation

The gentle shaking motion that avoids the formation of lumps, also prevents the damaging g-forces of high-frequency fluid bed designs. The reciprocating motion is a very gentle, yet robust way of moving the fluid bed as well as the product inside. This generates a maximum of one g-force on the material, instead of the eight g-forces prone to occur in high-frequency fluid beds. As a result, less stress is generated on the product, leading to less waste and optimal quality.

Also, the plug-flow characteristics of the Ventilex drive mechanism provide predictable residence time when drying natural fertilizer. Moreover, our proprietary control algorithm adjusts temperature and residence time to ensure that the fertilizer is dried to specification without overdrying or wasting thermal energy.

Minimize fertilizer production energy consumption

Our fluid bed organic fertilizer dryers typically use 30% to 60% less energy – the lowest energy consumption among dryer brands. This is in part because we recycle the waste heat from the cooler exhaust to the dryer area.

Minimize maintenance and downtime

Natural fertilizers are notoriously abrasive. However, yearlong experience has taught us which materials to use when building the corrosion-resistant equipment that can handle these products. European Excellence backs our rugged stainless-steel construction in Engineering and Manufacturing. Moreover, the simple mechanical design of a Ventilex fluid bed fertilizer drying machine, combined with its low-frequency drive and low g-force fluidization, results in less downtime.

As a result of the choice of materials and the unique mechanical design, a properly maintained Ventilex fluid bed organic fertilizer dryer will regularly exceed 98% scheduled availability. This feat is backed by customers, who indicate that both the installation and maintenance costs are significantly lower than with competitive designs.

Remove odor nuisance

Ventilex equipment offers odor nuisance relief in two separate ways. First of all, upon the completion of the drying process, the exhaust air is filtered to remove dust and odors. However, we also offer a second exhaust gas treatment option: wet scrubbing. Our two-stage scrubbing system consists of an acid stage, followed by an alkaline stage.

The acid stage of the scrubbing system
During the acid stage of the scrubbing system, a chemical reaction between the sulphuric hydrogen molecule and the alkaline free electrons takes place (-N), absorbing the ammonia. The corresponding indicative acid consumption depends on the ammonia range (technical-grade sulphuric acid is 96%).

The alkali-peroxide stage
The second stage of the scrubbing system, further reducing the acid odor and the NOx, is the alkali-peroxide stage. When opting to utilize the scrubber oxidatively, hydrogen peroxide will be added. The chemical reaction between the acid hydrogen molecule (or aldehyde) and the caustic soda hydroxide group (NaOH) will lead to the absorption of the formaldehyde and the volatile organic fatty acids.

Hydrogen peroxide will lead to exhaustive degradation of the stronger aldehydes. It will absorb these and ´break down´ the larger chains into smaller chains and radicals (predominantly acids). This oxidative stage is crucial in the removal of odors. Alkali is also added to bind the smaller chains and radicals.

Tailor-made and optimized in our Test Center

Over the years, Ventilex has delivered numerous fertilizer drying machines, such as chicken manure dryers, cow dung drying machines, peat dryers and so on and so forth. Because of the various ways fertilizers can be produced, we offer tailor-made solutions, at times fully integrating a dryer into an existing organic fertilizer production process.

For instance, one client needed to clean the exhaust air coming from the dryer by means of a wet scrubber, before reintroducing the air into the process. Other clients required cleaning of the exhaust air via a cloth filter, or a dust collector.  In many cases, the material from the dust collector is reintroduced into the final product, thus minimizing waste.

In most cases, our dryers are optimized before taken into commission – either in our test center in Heerde, the Netherlands, or at the customer’s production site. For example, our test engineers fed the control algorithm with client-specific processing data, teaching it how to adjust temperature and residence time according to specification. In another example, we built an iterative model to establish conditions that would prevent post-production drying from occurring, taking into account the fertilizer drying and cooling rates, and the effect of coating oils on the drying mechanism.

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Optimize your fertilizer production process

Would you like to find out how our test engineers can help optimize your organic fertilizer production process? We can test your fertilizer product and optimize its drying process in our test center in Heerde, the Netherlands. Alternatively, we can visit your site to optimize your current drying process.

Would you like to learn more about our organic fertilizer dryer? Or do you have any questions about this article? Feel free to contact us at any time!

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