Process Support Systems Overview for Photovoltaic Solar Cell Manufacturing

OVERVIEW OF PROCESS SUPPORT SYSTEMS
FOR THE PHOTOVOLTAIC SOLAR CELL
MANUFACTURING INDUSTRY

A white paper by Wastech Controls & Engineering, Inc.

Waste Water Treatment

Acid Waste Neutralization (AWN) systems adjust the pH of process waste water to within acceptable limits (typically 6 – 9) before discharging to the facility sewer connection. Reagent chemicals such as Caustic Soda and Sulfuric Acid are metered into reaction tanks at a rate proportional to the difference between the measured pH value and the target set point. Waste water sources may include process tools, de-ionized (DI) Water regeneration waste and scrubber blowdown. Incorporating the latest innovations in control strategy, such as feed forward control and hybrid mixing design, allow these systems to offer excellent performance and reliability with a smaller footprint and reduced chemical consumption with than traditional system designs.

Design Criteria:

Influent pH range of 2 to 12
Flow rates from <1 gpm to 400+ gpm

Configuration Options:

Batch or Continuous
Single, Double or Triple Reaction Stages
Molded or Fabricated Plastic Tanks or Fiberglas (FRP) Tanks
Air Operated Diaphragm (AOD) or Electronic Chemical Metering Pumps
Tank Mixers and/or Recirculation Pump Mixing
Reagent day tanks or supplied direct from drums or totes
Automatic return of off-spec treated waste water to eliminate discharge violations

Control System Options:

Programmable Logic Controller (PLC) or Relay Controls
Influent permissive dry contacts for interlocks with upstream equipment
Common trouble alarm dry contacts for remote alarm notification
Paper or electronic data logging
Ethernet LAN communication for PLC controls
Building Management System (BMS) integration

HF Removal systems treat HF-bearing waste water from process tools, when the fluoride levels exceed allowable discharge limits. These batch treatment systems use reagent chemicals such as Calcium Chloride and Calcium Hydroxide to precipitate the fluoride ions. Following treatment and settling, the clear water is decanted to an AWN or discharged, and the sludge waste is separated by filtration for solid waste disposal.

Configuration Options:

Flow rates from <1 gpm to 40 gpm with effluent concentration < 20 ppm
Single or Multiple Batch Treatment Tanks

Control System Options: see AWN

Heavy Metal Removal systems treat rinse waters from Plating lines used to add soldering contacts to PV wafers. These rinse waters are acidic in nature and contain heavy metals such as copper, nickel and tin. Heavy Metal Removal can be a batch or continuous system, and uses a combination of pH adjustment, precipitation, flocculation, clarification and filtration to remove heavy metal oxides. Reagent chemicals may include Sodium Bisulfite, Sodium Metabisulfite, Sodium Thiosulftate, Ferric or Ferrous Chloride (among others) in addition to pH adjustment using Sodium Hydroxide and Sulfuric Acid. Wastech also offers the MetFloc™ chemical line that reduces the process steps, lowers chemical consumption and minimizes sludge generation. Using MetFloc™ simplifies the control strategy, requiring only pH adjustment; it does not rely on other measurements such as oxidation reduction potential (ORP). The clear water can be routed to an AWN or discharged directly, depending on the discharge limits. The filtrate is disposed of as solid waste.

Design Criteria:

Flow rates from < 1 gpm to 100 gpm
Influent metal concentration range of 10 to 1,000+ ppm
Effluent metal concentration range of < 1 to 10 ppm

Configuration Options:

Batch or Continuous
Traditional reagent chemical supplies or MetFloc™ chemicals
Molded or Fabricated Plastic Tanks or Fiberglas (FRP) Tanks
Reagent day tanks or supplied direct from drums or totes
Integral post-treatment pH adjustment prior to direct final discharge

Control System Options: see AWN

Concentrated Bath Treatment is used to treat concentrated acid solutions received from the cleaning baths found at the start or in the intermediate steps of a Plating Line, or from the baths of a Rack Strip tool (located downstream of a Plating Line). These solutions often exceed 10% strength of Sulfuric or Nitric acids and have high concentrations of heavy metals. While discharges from the baths may be infrequent or periodic, the solutions cannot be treated by the AWN or Heavy Metal Removal systems due to the strong acid concentration, and they are often collected for off-site disposal. The Concentrated Bath Treatment System can accept these concentrated solutions, and neutralize them in batches to the point where the waste can be metered into a Heavy Metal Removal system.

Design Criteria:

Flow rates from < 20 gpd to 1,000 gpd

Configuration Options:

Molded or Fabricated Plastic Tanks or Fiberglas (FRP) Tanks
Reagent day tanks or supplied direct from drums or totes

Polymer/Photo-Resist Filtration systems are used to remove the polymer materials that are etched off of wafers following a screen printing and chemical vapor deposition or plating step. These materials precipitate out of waste water with low pH and increase turbidity to the discharge. This filtration system accepts batch dumps from etching tools, and then reduces the pH to facilitate filtration. The solution is pumped through filter bags and discharged to an AWN. The solids are collected in the filter bags and disposed of as solid waste.

Design Criteria:

Flow rates from < 20 gpd to 1,000 gpd

Configuration Options:

Molded or Fabricated Plastic Tanks or Fiberglas (FRP) Tank
Reagent day tanks or supplied direct from drums or totes

Control System Options: see AWN

Ion Exchange (IX) is used to reclaim and reuse DI Water from rinse water waste. The system employs activated carbon filtration followed by Cation / Anion exchange to remove contaminant ions. This restores the water’s resistivity and allows it to be reused in the process. The system uses Sulfuric Acid and Caustic Soda to regenerate the cation and anion resins. Inlet and outlet conductivity is measured to control the regeneration cycles and product water quality. The cation and anion resin canisters feature the Kinetico ® valve, which manages the counter-current regeneration cycles automatically. This patented valve technology eliminates dozens of actuated valves, simplifying system design and controls, as well as reducing consumption of regeneration chemicals. Standard systems are equipped with carbon filters, 5-micron filter bags at the inlet and outlet of the cation and anion canisters, and a UV lamp reactor at the discharge.

Design Criteria:

Flow rates from < 10 gpm to 100 gpm
Product Water Resistivity from 0.5 to >10.0 M-Ω cm

Configuration Options:

Redundant, parallel skid arrangements
Reagent day tanks or supplied direct from drums, totes or shared bulk supplies

Control System Options: see AWN

Waste Collection

Concentrated Acid Waste Collection systems receive batch dumps of concentrated acid waste water (typically > 10% strength), and then transfer the waste to drums or totes for off site disposal. The acids present may be Hydrofluoric, Hydrochloric or Nitric. The drum cabinet is equipped with load cells to automatically stop the filling operation once a drum is full. This eliminates the need for a level sensor to be placed in the drum by an operator. Both the receiving tank and the drum cabinet are fully contained for personnel safety.

Design Criteria (standard system):

Receiving Tank Capacity: 275 gal molded PE
Transfer Pump: One (1) 1-inch diameter air-operated diaphragm (AOD) type
Drum Cabinet Capacity: One (1) 55 gal Chemical Drum
Secondary Containment: Welded PP

Configuration Options:

Larger Receiving Tank Capacity
Two (2) Drum Cabinets
Metering Pump transfer to separate HF Treatment or AWN system

Control System Options: see AWN

Solvent Waste Collection systems receive batch dumps of DI Water that contain appreciable amounts of flammable solvents, usually Isopropyl Alcohol (IPA). The solvent waste is automatically transferred into drums for off site disposal. These fire-safe systems are fabricated with stainless steel and either explosion–proof or intrinsically safe electrical components. Solvent waste may be delivered directly to the drums or to a receiving tank which will automatically transfer to drums, depending on the facility process requirements.

Design Criteria (standard system):

Fire-rated metal storage cabinet
Drum Cabinet Capacity: One (1) 55 gal Chemical Drum
Transfer Pump: One (1) stainless steel AOD pump with Teflon wetted parts

Configuration Options:

Receiving Tank with or without Secondary Containment
Two (2) Drum Cabinets

Control System Options:

Class 1 / Div II or Intrinsically Safe construction
Influent permissive dry contacts for interlocks with upstream equipment
Common trouble alarm dry contacts for remote alarm notification
Drum filling controlled load cells or ultrasonic level transmitter

Configuration Options:

Duplex Pumps
Alternate OEM Pumps and wetted materials to match chemical compatibility
Automatic air purging
Nitrogen blanket pressure regulator and flow controls
Pump operation on permissive/demand signal or pressure control
Constant flow with backpressure control and return to the supply container
Valve Manifold Boxes (VMB) for branch distribution within Fab area
Stainless steel fabrication for solvents such as IPA

Control System Options:

Programmable Logic Controller (PLC) or Relay Controls
Pump permissive dry contacts for interlocks with upstream equipment
Integrated controls for CDM and downstream VMB
Safety alarms for open doors, leak containment, low and high pressure, proof of flow, and others
Automatic supply pressure control
Common trouble alarm dry contacts for remote alarm notification
Ethernet LAN communication for PLC controls
Building Management System (BMS) integration

Pump Lift Stations are used to transfer process tool waste water from gravity-fed drain lines to treatment systems downstream. The lift stations may be located close to process tools, or remote from the fabrication area in a facility vault or yard area. The tank, pump and piping materials selection will be matched to the expected process conditions.

Pump Options:

Air Operated Diaphragm (AOD)
Vertical or Horizontal Centrifugal
Simplex or Duplex Configurations

Tank Options:

Tank capacities from 16 gal to 2,000 gal
Single Tank or with Secondary Containment Tank
Molded or fabricated plastic tank construction (PP, PE, PVDF, PVC or CPVC)
Stainless Steel Construction
With or without valve manifold enclosures

Control System Options:

Level point switches or continuous transmitters
Local or remote control panel
Upstream and downstream permissive signals
Flow and pressure indicators and/or transmitters
Secondary containment leak alarm

Process Cooling Water (PCW) provides cooling water to heat exchangers within process tools to regulate operating temperatures. Process tools require purified water (i.e., either reverse osmosis (RO) or de-ionized (DI) quality) as a medium for cooling to avoid product or tool contamination in the event of a heat exchanger leak. Wastech builds PCW skids that include the pumps, filters, heat exchangers and controls to supply cooling water at the flow rate and temperature required by the facility. The PCW fluid is cooled by heat exchange with the facility’s chilled water system.

Configuration Options:

Flow rates from 50 gpm to 2,400 gpm
Supply pressures from 20 psig to 110 psig
Multiple redundant stainless steel pump arrangements
Variable Frequency Drive (VFD) pump control
Stainless steel plate and frame heat exchangers
20 micron filter unit
Sch 80 PVC or Stainless steel piping
Nitrogen blanket pressure regulator and flow controls for vented systems
Expansion tank for closed systems
Powder-coated structural steel skid

Control System Options:

Programmable Logic Controller (PLC) or Relay Controls
Automatic supply pressure and temperature control
Common trouble alarm dry contacts for remote alarm notification
Ethernet LAN communication for PLC controls

Process Hot Water provides hot water in a closed loop to heat exchangers within wet bench tools that require elevated temperatures for wafer processing solutions. PHW skids include a gas-fired boiler, pumps, filters, expansion tank, water treatment chemical feeder and controls to supply heating water at the flow rate and temperature required by the facility.

Configuration Options:

Flow rates from 200 gpm to 300 gpm
Supply pressures from 20 psig to 100 psig
2 MMBTU to 5.4 MMBTU heat output capacity
Output temperatures up to 203°F (95°C)
Multiple redundant pump arrangements
Variable Frequency Drive (VFD) pump control
Powder-coated structural steel skid
Welded carbon steel piping
Expansion tank and chemical addition feeder

Control System Options:

Programmable Logic Controller (PLC) or Relay Controls
Automatic supply pressure and temperature control
Common trouble alarm dry contacts for remote alarm notification
Ethernet LAN communication for PLC controls

DI Water Heating is a heat exchanger package delivering hot DI water to wet bench tools that require direct filling or dosing of process solutions with DI water at an elevated temperature. The skid includes a titanium plate and frame heat exchanger, flow control valves and temperature controller. This system exchanges heat from a Process Hot Water (PHW) supply and a DI Water source.

Configuration Options:

Flow rates from 20 gpm to 40 gpm
Output temperatures up to 185°F (85°C)
Titanium plate and frame heat exchanger
PVDF piping
Welded polypropylene skid

Control System Options:

Programmable Logic Controller (PLC) or Relay Controls
Automatic supply pressure and temperature control
Common trouble alarm dry contacts for remote alarm notification

Process Utility Monitoring systems monitor key parameters (e.g. pressure or flow rate) for critical process utilities such as Compressed Dry Air (CDA), Nitrogen (N2) and process water. Measured values and alarms can be displayed locally or remotely. Air Dryer Automation System (ADAS) is a supervisory controller that monitors the Compressed Dry Air (CDA) supply to the facility and operates redundant compressor / dryer units at maximum efficiency. Facilities have two or more air compressor and dryer units to guarantee uninterrupted process tool operation. ADAS distributes load to air dryers based on time and alarms, thus reducing on-line time and service costs, and yielding significant electrical power savings. ADAS places redundant units on stand-by during periods of low CDA demand. It will also rotate the lead and lag status of each unit on a user definable schedule, so that operating hours can be evenly distributed among all units. ADAS will notify facility personnel of alarm conditions, and make emergency responses such as opening a back up Nitrogen supply line in the event of complete compressor or dryer failure.

Wastech Company Profile

Wastech Controls & Engineering, Inc. (Wastech) was founded in 1987 by Paul Nicolas and has been in continuous operation under the same ownership and management since then. Wastech has become a nationally recognized process system integrator, offering automated process equipment and control systems for industrial applications. Wastech is staffed by engineers experienced in system design, fabrication, installation supervision, start-up assistance, and operator training.
Wastech has specialized in turn-key packaged systems for industrial waste water treatment applications in semiconductor, solar cell, pharmaceutical, biotechnology, metal plating and food processing facilities. Wastech offers a complete line of pump lift stations, specialized chemical mixing, batching, blending and dispensing packages, process cooling and heating systems, and process control panels in addition to fully automated waste treatment processes, such as pH neutralization, vacuum distillation, advanced oxidation and ion exchange.
Wastech has a UL508-approved panel fabrication shop with a reputation for reliable electrical and control designs with a high level of craftsmanship. Wastech is a Solution Provider for Allen Bradley and Rockwell Automation components and software.
Wastech is a certified member of the Control System Integrators Association (CSIA), which means that an auditor has evaluated Wastech’s business practices to insure that they conform to the CSIA’s Best Practices and Benchmarks. See www.controlsys.org for more information.
Wastech has developed its own blend of waste treatment MetFloc™ chemicals through the Pavlos Chemicals Company. These products offer surprising performance and cost effectiveness for removing heavy metal and other contaminants from waste water.
Our experienced team of engineers and supplier partners insure that our solutions are delivered on-time and perform beyond the customer’s expectations.