It might sound too good to be true: A batch plant that has a lower upfront capital cost, lower maintenance, and less operating cost, all while delivering well mixed, homogenous batch reliably to your furnace, writes Brian Naveken of Toledo Engineering Co Inc., (TECO).
And as most glassmakers will attest, optimised quality batch means that the furnace melts more consistently, enabling your furnace to operate at peak performance.
These batch plants are production proven over the years but with continuous improvement principles applied, they have become the ideal choice for delivering superior returns on investment.
Such batch plants are generically called 'compact' or 'vertical' batch plants, and they are an excellent example of how successful glass producers are rediscovering value by focusing on total lifecycle cost (or Total Cost of Ownership).
The main defining feature of compact batch plants is that they rely more on gravity versus mechanical conveyance, which is typical of 'horizontal' or 'in-line' batch plants.
Interestingly, compact batch plants are more prevalent in North America while in-line batch plants are more typical in Europe and Asia.
While the compact batch plant concept is not new to the glass industry, TECO’s CLEARbatch (Compact, Low cost, Efficient, Accurate, Reliable) is a next generation design consistent with TECO’s legacy of total value engineering and continuous improvement.
As there are elements of customisation in any batch plant design (for example, compact batch plants that use concepts more commonly found in-line batch plants and vice versa) direct comparisons can be fraught with caveats and special considerations.
Nevertheless, the intent of this article is to compare some of the more salient differences between compact and in-line batch plants with the intent of rediscovering the number of alternatives available to capital delivery decision makers in search of solutions to lower the total lifecycle cost.
The batch plant in Figure 1 (above) is a typical medium to high capacity batch plant for soda lime or similar glass chemistries.
It is what is referred to as a compact style batch plant, where raw materials are elevated and stored in silos located above the weighing and mixing process systems.
All raw material storage silos are designed to emulate mass flow of each material to minimize particle segregation within the individual raw materials.
By utilising a compact style batch plant, with raw material storage elevated, material can flow through the weighing and mixing systems using gravity to minimise the use of mechanical equipment.
This concept minimises the upfront capital costs, ongoing operational and maintenance costs, and the potential of abrasive wear within the equipment, which can contribute to contamination in the mixed batch delivered to the furnace.
Layout of the Structure
The nomenclature of ‘compact’ and ‘in-line’ reflects the layout of the batch plant, with the silos ganged together in the compact batch plant design, and alternately the in-line batch plant having the silos arranged in a line, which dictates a greater structure footprint (and cost).
Both compact and in-line structures can utilise either steel or concrete construction.
The major differences between the two batch plant styles can be found in the raw material unloading systems, the layout of the structure and the weighing systems. A complete comparison can be found in Table 1 below.
Figure 2 below illustrates a compact style batch plant and Figure 3 (bottom) illustrates an in-line batch plant.
The major differences between the two batch plant styles can be found in the raw material unloading systems, the layout of the structure and the weighing systems.
Raw Material Unloading System
A compact batch plant typically has only one unloading system for raw materials, although pneumatic unloading is also available for handling minor and/or micro batch materials.
On the other hand, an in-line batch plant has multiple unloading systems.
The raw material unloading system is typically comprised of the following components:
- Unloading shed – designed to protect against environmental contaminants;
- Unloading hopper – designed to provide complete clean-out of each material and avoid cross-contamination;
- Central dust collection system – for health and safety;
- Bucket elevator – reliable and designed to handle all materials;
- Rotary distributor – designed with reliable seals to prevent leaks and dusting.
Needless to say, the duplication of equipment associated with the in-line batch plant leads to increased equipment cost, more maintenance, and more potential for dusting.
In a compact system, multiple silos feed a single major and/or minor material scale using cumulative weighing control whereas an in-line batch plant typically has a multiple scale system, one for each raw material.
A weighing system is comprised of the following components:
- Weigh feeder – 2-speed to provide required capacity and slow feed for cut-off accuracy;
- Scale hopper – designed to provide complete clean-out to avoid cross-contamination and pressure balanced to protect against pressure influences that could affect accuracy;
- Scale system – digital electronic load cells with adjustable summing box and digital indicator compatible with the PLC control system.
Hence, there is a larger quantity of equipment items in an in-line batch plant.
Not only is there additional capital cost associated with this extra equipment, but the more equipment, the more maintenance that is necessary.
Also, the greater the number of discharge or transfer points, the more dusting that will be experienced.
- What level of redundancy is desired? The TECO CLEARbatch batch plant is equipped with only the necessary equipment required for reliable operation. This results in low capital cost, reduced maintenance and reduced potential for dusting;
- There is more attention to the operation of a compact batch plant due to the reduction of equipment items required. For example, if a bucket elevator belt breaks or a mixer transmission fails, the timing for repair is more sensitive if the supply of batch to the furnace is to be maintained. While this does tend to put more pressure on plant operators, a collateral benefit is that more attention is fixed upon batch plant operations to head off potential problems which more broadly results in better batch plant performance;
- Due in part to the considerations above, some decision-makers opt for in-line designs; however, it is important to note that compact batch plants have developed over the years to the point where the reliability and repeatability of even the older designs are well proven;
- Most up-to-date compact batch plants, and certainly the TECO CLEARbatch, are designed to make maintenance both easy and fast;
- There are many other benefits attributable to a compact batch plant. For example, the fewer pieces of equipment results in a decreased need for spare parts, maintenance personnel to perform the associated maintenance, and decreased potential for dusting due to decreased transfer points, just to name a few;
- Compact batch plants are production proven and have been in use for over a century. The TECO CLEARbatch compact batch plant is the culmination of decades of continuous improvement and innovation.
When compared to in-line batch plants, compact batch plants are particularly well known for better return on investment, lowest total lifecycle cost while providing batch quality that enables peak furnace performance.
The value of compact batch plants versus in-line can be summarized as follows:
- Minimum transfer points resulting in less dusting, less wear and less contamination;
- Smaller footprint, less expensive to go up than go out with less civil and construction cost;
- Less equipment required means less capital cost, maintenance and operating cost;
- Utilization of gravitational energy (free) for flow movement versus using mechanical energy to move flows left and right;
- In-line batch plants are typically easier to modify for large increases in production throughput and storage capacity, although compact plants are typically designed so that cycle times can be adjusted for increased throughput;
- Because compact batch plants do not typically have the same quantity of equipment items as in-line batch plants, designs to enable quick and trouble-free maintenance are employed to ensure batch plant reliability.
The TECO CLEARbatch/ compact style of batch plant, mixed batch and cullet processes are designed and selected for final batch and cullet quality delivered to the furnace, minimised upfront capital cost, minimized maintenance requirements, lower operating costs and maximum longevity and lifetime of the structure and processes.
Due to lower quantities of equipment and a smaller footprint coupled with years of engineering improvements produces a batch plant that adds value to your glass plant.
For decision makers focused on lowest lifecycle cost, compact batch plants are the preferred alternative to in-line batch plants.
TECO Group, www.teco.com