Wenger AquaFlex® Extrusion System coupled with surge and live bins, High Intensity Preconditioner (HIP), Dual Die Assembly, and Overhead Rail System
Twin screw extrusion
T
Wenger revolutionises twin screw extrusion with unique models dedicated to pet food and aqua feeds by Adrian Martinez-Kawas, PhD, Wenger Manufacturing
raditional twin-screw extrusion design has served its purpose as the pet food and aqua feed industries developed. Yet both industries now stand at a tipping point where new trends are pushing the traditional systems beyond their limit. Flexibility is key and what the new generation Wenger twin screw extrusion systems are built on. The Thermal Twin® extrusion system is tailored for pet food manufacturers, so they can develop a wider range of products using an extensive choice of ingredients while preserving ingredient and product identity. The Aquaflex® extrusion system is tailored for aquatic feed manufacturers to maximise their investment by giving them the capability to manufacture a wide range of products such as floating, sinking, shrimp, and micro feeds in different product sizes while utilising a broad ingredient selection. This flexibility is possible given these systems are engineered with a specialised screw profile design to deliver higher volumetric capacity and the capability to operate using a wide range of thermal and mechanical energy cooking conditions. Thermal and mechanical energy are the main energy sources utilised in the extrusion process. A review of current extrusion processes in the industry indicates the ratio of consumed thermal to mechanical energy ranges from 1:1 to 2:1. This ratio determines utility costs as well as maintenance costs, specifically the costs to replace worn rotating elements. A recent study compared energy input and operating cost for three extrusion system (See Table 1). It was observed that even though the total energy input (thermal + mechanical) was higher for a thermal twin screw extrusion system, it was less expensive to operate over time compared to a standard single screw and twinscrew extrusion system. An extrusion system with the ability to vary this energy utilisation ratio and shift to the most favorable energy sources from a cost standpoint, brings increased flexibility to the cost of operating the system. Wenger extruders are engineered to operate in thermal to mechanical energy ratios from 1:1 to as much as 14:1. This is achieved with a twin-screw profile that allows up to four-to-six times more steam injection into the extruder barrel. Additionally, these systems are coupled with a high intensity preconditioner (HIP) which provides less product moisture variation and increases the starch gelatinisation compared to other steam conditioning designs (See Table 2). As a result of a wider energy utilisation ratio and a specialised twin screw profile, coupled with a preconditioner which delivers less product moisture variation and increased cook, the flexibility
of the Thermal Twin® and Aquaflex® extrusion systems become key to increase product offerings. Thermal energy is considered a more natural way of cooking when compared to mechanical energy. This translates to less shear and more gentle kneading to continuously develop the visco-elastic dough product matrix. With a Thermal Twin® extrusion system, pet food manufacturers can go beyond the traditional dry expanded and offer high carb, baked, soft moist, vegetable bit inclusion, and high meat pet food. Furthermore, specialty treats (short and long), retort-stable wet food, engineered ingredients (up to 200% percent% wet meat slurry content), and textured vegetable/meat protein products can be manufactured with this type of system. With an Aquaflex® extrusion system, aqua feed manufactures can expand their offering to shrimp, floating, micro, sinking, and fish soluble inclusion feed. New generation twin screw extruder design and thermal cooking allow for a wider ingredient utilisation such as novel animal and vegetable protein sources. Not only is there a wider ingredient selection to work with, inclusion levels of ingredients such as fresh meat and slurries are two-fold in new generation Wenger twin screws extruders when compared to single screw Table 1: Energy input and operating cost comparison between Wenger single screw, twin screw and thermal twin screw extrusion systems Extrusion Systems
Single Screw
Twin Screw
Thermal Twin Screw
49.7
65.6
154.7
37
60
16
Total Energy (kWhr/mt)
86.7
125.6
170.7
Energy Cost ($/mt)
5.3
8.07
6.22
Specific Thermal Energy (STE, kWhr/mt) Specific Mechanical Energy (SME, kWhr/mt)
Wear Cost ($/mt)
2.1
3.41
0.91
Total Cost ($/mt)
7.4
11.48
7.13
Table 2: Percent of Coefficient of Variation of Moisture Content and Cook Using Different Steam Conditioner Designs Steam Conditioner Design
Coefficient of Variation of Moisture Content (%)
Cook (%)
HIP – High Intensity Preconditioner
2.65
30
DDC – Differential Diameter Cylinder
4.96
25.9
DC – Double Cylinder
6.66
20.4
SC – Single Cylinder
9.36
15.7
22 | November 2019 - International Aquafeed