Mustafa Yılmaz
Founding Director
Pusulay Mühendislik ve Danışmanlık

In this second installment of our three-part guide focusing on energy efficiency and low-cost manufacturing in feed mills, we examine the pelleting and conditioning processes, which account for the largest share of total energy consumption. Through empirical case studies, we analyze how technical parameters ranging from efficient steam conditioning and direct-drive presses to die-roller optimization and ration pelletability can yield improvements of 10–25% in electrical consumption and 5–25% in press throughput capacity.

PELLETING AND CONDITIONING

The pelleting process accounts for the highest share of total energy consumption in feed mills. One of the primary factors governing the energy performance of this process is the quality of conditioning. Introducing the appropriate temperature, moisture, and steam to the feed during the conditioning phase directly impacts both pellet quality and the power consumption of the pellet mill.

EFFICIENT STEAM CONDITIONING

Injecting high-quality saturated steam at appropriate pressure and temperature (typically 115–130 °C) during conditioning promotes starch gelatinization, contributing to the plasticization of the meal. Consequently, the feed passes through the pellet die with lower mechanical resistance, reducing the load on the press main motor.

Insufficient steam application, on the other hand, increases friction during pelleting, elevates mechanical stress on the die, and subsequently drives up electrical power consumption. Industrial field applications report that motor current can be reduced by 10–20% in pellet mills operating with properly conditioned material.

This trend has been confirmed by operational trials. In one trial, reducing the opening ratio of the proportional steam valve from 43% to 33% resulted in an increase in specific electrical consumption of 2.04 kWh/ton for the pellet mill—a rise of approximately 8.8%. These results demonstrate that steam volume in the pelleting process directly affects not only product quality but also energy efficiency.

Table 3. Effect of the amount of steam supplied on electricity consumption.
Note: Tests were conducted using the same raw material, the same pellet mill, and under the same operating conditions.

Technical Evaluation: Keeping steam volume below required levels may appear to reduce steam consumption in the short term; however, it increases mechanical load on the pellet mill, causing electrical power consumption to surge. Therefore, steam and power consumption must be evaluated jointly, and the process should be operated at an optimum duty point that minimizes total energy consumption.

STEAM VOLUME OPTIMIZATION

Every feed formulation possesses a distinct water- and steam-holding capacity. Therefore, the opening percentage of the proportional steam valve does not directly reflect the actual volume of steam absorbed by the feed. Dosing steam above real requirements leads to steam leakage through openings on the conditioner or pellet mill, increasing thermal energy losses. Furthermore, excess moisture negatively impacts pelleting stability and increases downstream drying requirements.

Consequently, steam control should not be optimized solely based on valve opening, but rather through a combined evaluation of product temperature, product moisture, press motor load current, and pellet durability index (PDI).

DIRECT-DRIVE PELLET MILLS

The drive system utilized in pellet mills directly influences mechanical energy efficiency. Mechanical losses inherent in conventional belt-pulley or standard gearbox-driven systems are significantly reduced in direct-drive or high-efficiency torque motor systems.

In literature and field trials, these systems are reported to achieve electrical energy savings of 5–15% compared to conventional drive systems. Additionally, reduced maintenance requirements and more stable torque transmission represent key operational benefits that enhance plant reliability.

DIE THICKNESS AND EFFECTIVE PRESSING LENGTH

Pellet die thickness and effective pressing length are primary parameters determining the mechanical load exerted on the press main motor.

Selecting dies thicker than necessary forces the feed to travel a longer distance inside the die hole, increasing the press load and consequently raising electrical consumption.

Therefore, die thickness should be specified by taking into account feed formulation, pellet diameter, target PDI value, and production throughput. Selecting the proper die not only reduces energy consumption but also improves press capacity and pellet durability.

BYPASSING PRE-COMPACTION EQUIPMENT

In certain facilities, pre-pelleting systems, Boa compactors, or expanders are utilized prior to the main pellet mill to achieve high pellet durability (PDI).

However, keeping this pre-compaction equipment continuously online for all feed formulations is unnecessary. Bypassing pre-compaction equipment, particularly for products where target PDI values are easily attained, eliminates extra electrical consumption and contributes directly to overall energy efficiency.

To evaluate the feasibility of this practice economically, both operational scenarios should be analyzed across the following parameters:

• Electrical energy consumption (kWh/ton)
  
• Press throughput (tons/hour)
• Pellet durability (PDI)
• Steam consumption

MONITORING DIE AND ROLLER WEAR

Wear on dies and rollers, degradation of hole entry countersinks, or hole blockage reduces pellet mill throughput and causes the main motor to draw higher current.

Regularly monitoring dies and rollers based on operating hours or processed tonnage—and replacing components that have reached their wear limit in a timely manner—reduces energy consumption while preventing unplanned downtime.

ADJUSTING FEED DEFLECTOR BLADES

Feed deflector blades located at the pellet mill inlet are critical components that ensure uniform distribution of the meal across the die face.

If blade angles or positions are incorrectly adjusted, the entire surface area of the die cannot be utilized effectively, leading to capacity losses and forcing the press motor to operate under higher mechanical loads.

During periodic inspections, uniform pellet extrusion across the full face of the die should be confirmed and necessary adjustments executed.

TARGET PELLET DURABILITY INDEX (PDI) OPTIMIZATION

Pellet Durability Index (PDI) is a vital indicator of feed quality. However, establishing PDI targets above actual requirements frequently results in unnecessary energy consumption and throughput losses.

Optimizing target PDI values in alignment with customer expectations and product end-use can yield substantial energy savings.

In executed trials, reducing the target PDI value from 97.0 to 96.5 resulted in:

• A 10–20% increase in press throughput
  
• A reduction in electrical energy consumption of approximately 2 kWh/ton (~10%)

These findings indicate that establishing an optimum PDI level that fulfills structural quality requirements is essential for energy efficiency.

OPTIMIZING DIE HOLE COUNT AND OPEN AREA RATIO

The number of die holes and the total open area ratio are key design parameters directly impacting press capacity and energy consumption.

Dies with a low open area ratio restrict feed passage, increase mechanical resistance on the press, and raise electrical power consumption.

In one comparative trial evaluating two dies with identical geometry but a ~10% difference in hole count, the die with the higher hole count delivered:

• 5.6% higher production throughput
• 23% lower electrical energy consumption

These results underscore that total open area ratio—not just hole diameter—is a critical criterion for energy efficiency in die selection.

Table 4. Effect of the number of pellet press die holes on pelleting performance and energy consumption.
Note: Tests were conducted using the same raw material, the same pellet press, and under the same operating conditions.

EFFECT OF RATION COMPOSITION ON PELLETABILITY AND ENERGY CONSUMPTION

The physical and chemical properties of raw materials used in feed formulations directly influence pelleting performance and energy consumption. The fiber structure, starch content, fat percentage, and natural binding characteristics of ingredients play a decisive role in both pellet durability (PDI) and the mechanical load on the pellet mill.

Ingredients with high natural binding capability such as wheat bran, wheat middlings (bonkalite), and molasses enhance pellet durability, reduce friction within the die holes, and allow the press to operate under lower motor load.

Similarly, raw materials such as rice bran and full-fat soy, by virtue of their natural oil content and physical structure, facilitate material flow through the die, thereby increasing pellet mill capacity and reducing specific electrical consumption.

Conversely, materials that are inherently more difficult to pellet—such as DDGS, corn grit, and barley, increase mechanical friction on the press, which can lower throughput and elevate energy consumption. Therefore, when formulating rations, processing characteristics (processability) must be evaluated alongside nutritional composition.

In practical trial studies, adding 3% rice bran to the formulation yielded an approximate 25% increase in pellet mill capacity and a 14% reduction in specific electrical consumption. These findings prove that proper raw material selection significantly enhances not only pellet quality but also production throughput and energy performance.

Table 5. Effect of including 3% rice bran in the formula on pelleting performance and energy consumption.
Note: Tests were conducted using the same raw material, the same pellet press, and under the same operating conditions.

Technical Evaluation: Ration optimization must be evaluated not only for cost and nutritional value, but also for pelletability and energy efficiency. In many cases, incorporating functional ingredients or natural binders that enhance pelleting performance can offset their additional raw material cost through realized energy savings and throughput gains.

SUMMARY: KEY FACTORS INFLUENCING ENERGY EFFICIENCY IN THE PELLETING PROCESS

The pelleting process represents the single largest consumer of electrical energy in feed mills. Conditioning quality, equipment specification, mechanical settings, and ration composition directly govern press capacity, pellet quality (PDI), and specific electrical consumption. The field examples and trial data presented in this section summarize viable energy efficiency strategies and their operational impacts. Implementing proper process optimizations can yield improvements of 10–25% in electrical consumption and 5–25% in press throughput.

These results prove that energy efficiency is achieved not only through capital equipment investments, but also through rigorous process management, optimized operating parameters, and data-driven operational decisions.

Pusulay Engineering and Consultancy draws upon 21 years of industry expertise and engineering methodologies to analyze operational processes and deliver engineering, operations management, and efficiency-focused consulting services to the feed sector.

We continue to support feed milling enterprises through practical solutions in shrinkage and loss management, energy efficiency, operational cost optimization, capacity expansion, downtime and failure reduction, site audits, feed mill engineering investments, feasibility studies, regional market research, and operational SWOT analyses.