Process Modeling for Plating Energy Usage
A look at finishing energy costs and tips to help you cut them
Besides labor, the major operating costs of surface finishing facilities are related to materials, energy usage and environmental compliance. This article will examine material, energy, and environmental cost models and the relative cost of energy usage for three diverse surface finishing facilities. The three facilities include a high-volume hard anodizing shop, a high-volume decorative anodizing shop and a shop that performs a variety of low-volume plating and anodizing operations.
The first facility, a hard anodizing shop, produces 6 loads/hr on two automated process lines utilizing three automatic hoists and one wet shuttle. Process solutions are heated with low-pressure steam, and process cooling is via a low-efficiency chiller. Process solutions are air-agitated, and air is supplied by a 150-psi compressor.
Process tanks are equipped with automatic covers. The ventilation system uses automatic dampers to ramp the ventilation rate between 10% (cover closed) and 100% (cover open) of design capacity. Plant makeup air is tempered to control temperature and humidity and maintain a slight positive pressure in the plant.
Facility 2, the high-volume decorative anodizing shop, produces 24 loads/hr on five process lines using 16 automatic hoists. Process solutions are heated with electricity, and process cooling uses a low-efficiency chiller. The process lines include 31 dye tanks and nine seal tanks. Process solutions are agitated with pump/eductor systems. Process rinses are air-agitated, and air is supplied by a low-pressure air blower. Plant makeup air is un-tempered and supplied by a passive system.
Facility 3 is a low-volume, diverse functional plating and anodizing shop. It produces 10 loads/hr of mixed plating and anodizing on 10 automated process lines. Process solutions are heated with low-pressure steam, and process cooling utilizes a high-efficiency chiller. Process solutions are agitated with pump/eductor systems. Rinses are agitated with air supplied by a low-pressure air blower.
Each process line is equipped with a segregated ventilation system. Plant makeup air is tempered to control temperature and humidity within a segregated operator setup area maintained at a slight positive pressure relative to separate wet and dry process areas. Process heating, cooling, agitation and filtration are managed by a sophisticated energy management system.
In these three shops, total energy usage accounts for 33-54% of non-labor operating costs. Total environmental costs account for 2-8% of non-labor operating costs, and total material costs account for 44-59% of non-labor operating costs. The breakdown of total material, energy and environmental costs within the three facilities is reasonably consistent; however the detailed breakdown of costs within each category varies significantly.
Material cost components in our models included water, drag-out, dumps or bleeds, coating, and other costs, such as masking materials. Environmental cost components included on-site treatment, off-site treatment, effluent, and waste disposal.
The modeling indicates that energy usage is a major cost component of all three surface finishing operations. The remainder of this article will focus on surface finishing facility energy usage and cost, because the opportunity to reduce energy cost is greater than that for material or environmental costs.
A Closer Look at Energy
Energy usage can be broken down into several major groups. The first includes process heating, rectifiers, process ventilation and makeup air (heating/cooling/process ventilation).
Process heating costs in the three shops ranged from a low of 2% (Facility 1) to a high of 66% (Facility 2) of total energy costs. Process heating costs can be significantly reduced with proper tank insulation, automatic (or manual) tank covers, and the use of energy management systems to control tank temperature and agitation when tanks are not in use.
Rectifier energy costs ranged from a low of 6% (Facility 2) to a high of 58% (Facility 1) of total energy costs within the three facilities. Rectifier energy costs largely reflect production requirements, but energy costs can be reduced with power factor management, minimization of bussing runs, and use of low-resistance electrodes (aluminum rather than lead) in anodizing.
Process ventilation costs range from a low of 4% (Facility 1) to a high of 23% (Facility 3) of total energy costs within the three shops. Process ventilation costs can be significantly reduced with the use of automatic tank covers and dampers and by installing variable-frequency drive (VFD) motors, where the ventilation rate is modulated depending on whether the cover is open or closed.
Ventilation rates can also be reduced with push/pull ventilation, back shields and/or optimization of tank aspect ratios. Scrubbers increase the static pressure in a ventilation system, and “vent only” requirements should be segregated from air pollution control systems (scrubbers and mist eliminators) whenever possible. Rates can also be reduced in enclosed process lines where operator exposure is minimized and ventilation capture efficiency is optimized.
Makeup air costs range from a low of 0% (Facility 2) to a high of 23% (Facility 3) of total energy costs in the three shops. An effective positive pressure, makeup air system can reduce the static pressure of the ventilation system and improve capture efficiency and operator comfort, and reduce plant and equipment corrosion.
The second major grouping of energy costs we studied included process agitation/filtration, process cooling and process material handling (hoists).
Agitation/filtration costs ranged from a low of 3% (Facility 3) to a high of 8% (Facility 1) of total energy costs. Compressed air agitation is significantly (an order of magnitude) more expensive than low-pressure air as a means of air agitation. Agitation and filtration costs can also be reduced with an energy management system that agitates process tanks only when parts are in the tanks (process and rinse tanks) and mixes solutions when tanks are heated or cooled to assure good heat transfer.
Process cooling costs ranged from a low of 1% (Facility 3) to a high of 8% (Facility 1) of total energy costs in the three shops. High-efficiency chillers use significantly less energy than low-efficiency units, and the ROI from replacing old chillers is normally very favorable.
Process material handling costs—that is, the costs of operating hoists—ranged from a low of 4% (Facility 3) to a high of 5% (Facility 1) of total energy costs within the three facilities.
We did not include the third major group of energy costs Group Three in our modeling, but these costs include process fluid handling (wastewater collection and treatment, chemical makeup, process water, etc.), heat treatment and drying.
|Agitation & Filtration||8%|
|Total Energy Cost|
As can be seen from the Table, it is difficult to make generalized statements about energy usage within surface finishing facilities. Process modeling is a very effective tool for characterizing energy usage on an activity basis and prioritizing improvement projects.
An effective process model facilitates detailed analysis of plant energy costs by enabling users to look at each cost individually. In Facility 2, for example, modeling identified the sealing process as the greatest consumer of energy (40%, of the total, or $220, 119). Looking deeper, process heating accounts for 89% or $196,416 of sealing process energy usage. Clearly, optimization of sealing process heating is the biggest opportunity to reduce energy consumption in Facility 2.
Our process modeling showed that the largest consumers of energy in the three shops examined can all be impacted with proper line design and operation. Here’s a look at the top energy consumers in the three shops examined.
Process heating is, on average, the largest energy consumer in all three facilities. Energy costs vary significantly depending on the specific processes being performed and production requirements. Process heating costs can be controlled with good design and management. This is one of the most important areas to focus on for energy cost reduction.
Process rectifiers are second only to process heating as an energy consumer. Again, energy costs vary significantly depending on processes and production requirements. Process rectification costs are difficult to reduce significantly; however, good process control can minimize over-plating and coating rework. To the extent that process efficiency can be managed, this can reduce rectifier costs significantly.
On average, ventilation is the third-largest energy consumer. Again, energy costs vary significantly depending on processes and production requirements. Process ventilation costs can be controlled with good design and management.
The fourth-largest energy consumer is makeup air, but energy costs vary significantly depending on processes, production, and facility requirements. Process makeup air costs are a function of ventilation requirements. Good ventilation design and management will reduce makeup air costs.
Process agitation and filtration is the fifth-largest energy consumer, but energy costs vary significantly depending on processes and production requirements. Process agitation and filtration costs can be controlled with good design and management.
Sixth-largest on the energy consumption list is process cooling. Process cooling costs can also be influenced with good design and management.
Process material handling is, on average, the seventh-largest energy consumer in the three shops. Again, energy costs vary significantly depending on processes and production requirements. Process material handling costs are difficult to control, but good process layout will reduce hoist travel and energy usage.
Based on process modeling, we can make some recommendations to reduce energy costs that many shops can easily implement.
To reduce process heating and other costs, do not heat, cool, agitate, or filter solutions when not required. Make sure tanks that are heated and/or cooled are properly insulated.
Do not ventilate processes that do not need ventilation, and do not scrub ventilation when vent-only (moisture removal) will serve.
A well-designed and balanced ventilation and makeup air system can reduce energy usage, minimize facility corrosion, and improve operator comfort and safety. Automatic tank covers can minimize ventilation, heating, and cooling requirements.
To minimize rectification costs, optimize process solution efficiency, voltage drop, and over-plating.