Table of Contents
Introduction
The high level of global plastic use has led to an increasing procurement of discarded post-consumer plastic material, and there is a demand for a process strategy to best depolymerize and repolymerize it. Here, we are concentrating on the reprocessing of post consumer used plastics into consumer products, using the various reprocessing methods which are possibly available for a new venture business. With the usage of this reprocessed plastic material, there exists methods to physically recycle the plastic into a direct form of consumer product, these methods exploit the plastic’s thermoplastic nature. A further method of recycling plastics is from an energy recovery approach, using the depolymerization process to break the polymer bonds and recover the low level energy value of various plastic materials. Whether using the latter energy recovery method to downcycle the plastic material into a fuel form, or the process of repolymerization to make a higher quality recyclate, both methods have the potential to save the environment from vast amounts of pollution caused by the careless disposal of plastics and reduce the industry’s demand for high levels of plastic production and the usage of fossil resources. The method choice greatly varies depending on factors like to which extent plastic material is to be recycled, the available funding, and the type of plastic material to be worked with. Due to the multiple forms of reprocessing methods, we have investigated machine concepts and strategies to accommodate the various methods, using said machines to best adapt and recycle plastic materials into forms suitable for further use.
Machine Selection
Reprocessing plastics will require machinery designed for the specific polymer type. The Society of the Plastics Industry has identified seven different plastic types (SPI Code) that may be present in the waste stream. It is a tough challenge to recycle plastics together due to the seven different resin identification codes, which is why sorting is usually preferred when recycling plastics. An extensive study was conducted to compare the compatibility of mixing different plastic types for the purpose of recycling. It was found that when recycling plastics within the same resin family (e.g. mixing some RPET and G-PET), the physical properties of the polymer are not significantly changed. This is due to the fact that polymers of the same family are likely to have similar chemical structures and melting points. The results will vary, however, when attempting to recycle two different plastic types. When heated above their melting point, polymers undergo a phase change wherein they go from solid to liquid. Upon subsequent cooling below the melting point, the polymer will solidify in a new shape or form, a process similar to ice melting and re-solidifying. Heating and cooling is a simple concept used in forming plastic parts and is also a primary method in recycling and regrinding plastics. If two different plastic types are mixed during the regrind process, the two will undergo phase change and likely solidify in a random blend of the two shapes. This may have detrimental effects on the physical properties of the plastic, taking away from its quality and potential uses. Whether or not this is an issue to a specific industry will determine how critical it is to use machinery for a specific plastic type.
Once the decision to recycle plastics is final, the next choice an entrepreneur faces is what type of recycling machinery to utilize. One of the ways to avoid this decision is to consider contracting a plastics recycling company that will process the material and return it to the producer. While this is an option, it can be extremely costly in the long run, taking away from the benefit of recycling by cutting into the potential revenues. The alternative is to purchase recycling machinery or, in some cases, refurbish used machinery. This decision is also not so cut and dry and is by no means simple. It is best to start with an analysis of the available recycling machinery along with a comparison of different machines and vendors. Ask the supplier if they have a technical data sheet of their machinery; this is a good way to start collecting information.
Capacity Considerations
When selecting the proper machine for plastic recycling, the primary consideration is the proportion of material you intend to process per unit time. If you are looking to recycle a very small quantity of material, the best recycling equipment to start with may be a simple granulator. This is a low-cost way to begin, and the material can be reprocessed into new consumer products at a later date. If a large quantity of material is to be processed, a more complex and higher output system is recommended. For example, a small to medium-sized recycler processing 10,000 lbs per day of mixed plastic waste may choose the following equipment configuration: 2 x 1000 lb/hr reclaim extruders, to produce roll stock sheet in-house, and 1 x 500 lb/hr reclaim extruder to reprocess its own internal waste. In this case, the customer would be considering the output capabilities of the machines to be purchased. If he were to buy 3 of the same 1000 lb/hr extruders, it would limit his flexibility and possibly his future growth, as he would not be able to reprocess other materials at a lower input cost. Matching the machine to the job activity that it must do is very important when considering machine output. A common mistake for a recycler is to purchase a machine with an output larger than what is necessary and assuming they can run it at full capacity to maximize payback. This may result in a less desirable product, higher reject rates, and difficulty in processing. Always look at the rate of the machine specified with the type of material to be processed. If there is any doubt, trial the material at 1/4 rate higher than the minimum required to give allowance for screw and press wear over time.
Material Compatibility
During washing processes, different plastics are subjected to various temperatures and caustic chemicals. Although the goal of cleaning the material is consistent across all types, the ramifications of the cleaning process differ greatly depending on the polymer. For example, PET is stable at lower temperatures with hot water, whereas PVC plastic becomes pliable. Washing PVC in this manner makes it difficult to remove contaminants because the plastic will tend to absorb liquid and swell. This is a common problem with many of the thermoplastic polymers. The mechanical action of the process is also very important. Friction washers are good for some plastics but often produce a large amount of ground plastic, making them unsuitable for many recycling processes. The ground plastic is often difficult to clean and results in a lower quality end product. Other plastics can be cleaned very effectively with hydrocyclone separators, but the high density of PET makes it difficult to float and thus separate using wet gravity methods. Avoiding over-exposure of the cleaned material to heat is the best practice. The drying of the material is also important. Polyester and PS can be dried at around 180-200°C, and for a very short time, whereas higher temperatures can cause thermal degradation. Step splayed twin screw extruders can effectively dry the material at lower temperature by increasing the surface area through conveyance in a vacuum. Overall, being able to run all the cleaned material through a single type of machinery is most effective in terms of both cost and end product quality. A thorough understanding of the behavior of polymer during washing and cleaning processes is important in order to be able to provide a system which effectively cleans the material and avoids damage.
Energy Efficiency
Finally, while implementing previous measures to check the energy used by a specific machine, it is important to monitor the overall energy usage of a plant and the machines within it. This will prevent damage to the environment from unchecked energy use and, more importantly, find if any change in machinery or process has had adverse effects.
Choosing energy-efficient machinery is a more straightforward process today, as high-efficiency equipment is becoming the industry standard. A generic approach to machine comparisons can be formed using energy costs and the use of energy performance indicators. An example of this is a study which compared injection molding machines by recording the energy required to produce one complete cycle of the machine. The machines were then rated by energy cost per cycle and categorized by size. A regression analysis found a correlation of machine size to energy efficiency, with a guideline of the large machine energy cost being 11% above the mean for each size category, all the way up to a massive 58% of small machine energy cost. The costs from this analysis can be loaded onto part costs, giving consumers clear information as to how energy efficient the machine being used is and where money can be saved. With the fast rate of new technology emergence, machines should be checked for efficiency at regular intervals to ensure that energy and money are not being wasted.
The aim of reducing energy consumption of machines is available capital in the form of money and energy. The most common measure of this is the capital cost per output capacity. An example from a processing plant which was designed to process 100,000 tonnes per year of extrusion grade HDPE using 7 machines, each with a 400-tonne screw capacity. The old design used standard AC motors and on/off controls on the machines. The conventional wisdom in the industry was that an output rate to screw capacity ratio of 20 was needed. This would dictate 15 machines, each with a 2000-tonne screw capacity. These would have been energy exorbitant, but instead high torque/low-speed screws were used, pushing the output ratio up to 30 for the same screw capacity. Using more energy-efficient motors, a power consumption of 0.12 kWh/kg was recorded, giving a total of 20 MWh. If paralleled with the first design, less energy would have been used despite the new design being cleaner and more energy efficient. This is because higher output rate machines inherently use less energy per unit throughput.
Machine Setup and Installation
Adequate space must be prepared according to the recycling machine’s specifications. Typically, a hard level surface is required with at least 2-3 meters clearance around the machine for operational and maintenance purposes. Standard incoming material conveyors are adjustable to suit the best height for feeding material into the machine. It is important to have the conveyors matching the machine height to prevent inclining conveyors. Incoming material from an incline conveyor does not feed consistently and can cause unnecessary wear to high friction machine feed components. Space should be considered for optional equipment such as feed conveyor metal detectors and discharge conveyors, as it is likely these options may be installed at a later date. High-speed machines and machines with large feed components such as sheet and large pipe may require the material to be pre-cut to suit the feed width. This can be achieved in an area external to the machine; however, it should be close by with easy access for the operator.
Section 3 for machine setup and installation provides valuable information for preparing to install a plastic recycling machine. These are general guidelines that best fit all machine types and must be followed unless specified by local regulations or the machine itself.
Location Requirements
The machine weighs a maximum of 9800 pounds (4445 kg). This includes everything: the hydraulic power unit, control unit, mechanical sorter, and the entire main unit and its components. The floor that the machine sits on must be able to support this weight. Failure to provide stable construction may cause the machine to shift during operation or machine maintenance. This may lead to undesirable machine operation and component malfunction. A level machine must be ensured with a maximum 2.5° tilt in any direction. This is to avoid machine operation problems and component malfunction. Any slope exceeding this limit will cause the machine to tilt, thus causing improper component operation or, worse, machine component damage.
Overhead clearance of 1 meter is the minimum size required. This is given for the ease of opening the machines and separating the components, and also to avoid the failure of the mechanical sorter, as it requires maximum space. The compressed air quality should be clean, dry compressed air of at least 110 psi. This is used in many components of the system, but the most air is consumed by the mechanical sorter, which has a maximum requirement of 45 cfm. The remaining air is used for the pneumatic valves used for process control. Since the mechanical sorter requires the most air in the entire system, an air quality of 110 psi and 45 cfm is necessary. An air demand higher than specified may cause the sorter to fail. During an abrasive separation trial, it was found that the higher the air pressure for the mechanical sorter, the better the separation efficiency. An air compressor with a 10 hp motor should be suitable for this air requirement.
Electrical Connections
A qualified electrical technician familiar with National, State, and Local codes should make the electrical connections. All wire connections must be tight and should be soldered and insulated to ensure safe and reliable operation. The integrity of the ground path must not be defeated. It is recommended that all printed wire boards have proper surge protection devices installed on the input power lines to protect against electrical damage of the printed wire board from external sources. A switch-type noise filter is recommended to suppress electrical noise generated by the machine and to protect other nearby equipment. Failure to do this could, in some cases, cause peripheral failure. Step-type voltage regulators (boost or buck-type transformers) may be needed in locales where the input voltage supply is not stable. It should be noted that static discharge can cause damage to electronic printed wire boards.
It is the responsibility and duty of the customer to carry out all necessary work to accommodate the electrical connections. Most of the standard machines have basic electrical requirements, excluding the Hopper Dryer Renew Unit, Sheet & Film Waste Recycling Ranges, Laboratory and Blown Film Waste Recycling Machines, which have specific requirements. These requirements would be discussed at the time of order if required. Please ensure all work is carried out by a qualified electrician and conforms to all municipal, provincial, and state laws. Also, ensure that the electrical connections are switched off before making any connections to the machine.
Safety Measures
All moving sections are enclosed to prevent unexpected accidents. Sensors are installed in the conveyor to stop the conveyor when it is overloaded. Emergency stop switches are provided at easy-to-access locations at the conveyor and the shredder/granulator. These steps are taken to safeguard workers when any repair or maintenance is performed, to ensure the worker is not accidentally injured when the machine starts up. Voltage monitoring relays are used to determine if there are any faults in the electrical system. This is to prevent any unexpected machine start-up due to voltage fluctuation. Last but not least, all control systems are designed with fail-safe relay logic. This is to ensure that all machines will automatically shut down in a safe manner when any fault is detected in the control system. By doing this, it will eliminate all possibilities of unexpected machine start-up due to electrical system errors. This will greatly reduce the accident level at the workplace. Safety is always a concern for everyone involved. With all the safety features, we ensure that our plastic recycling machines are safe to be operated and their reliability will ensure the safety of workers maintaining them in the long run.
Operating Procedures
Minimize the generation of waste by using the regrind and/or scrap in the same form it was produced before the waste. It may be necessary to requalify the use of the material for a particular application. If it is not feasible to process the reclaimed material, contact a similar processing application that can use the material. If the material is to be sold, post-consumer material sources may have requirements for the material quality. It is necessary to dry reclaimed material before processing. Follow processing recommendations from the material supplier or visit the website listed on the material container. Failure to process material at the recommended conditions may cause degradation and will limit the number of times the material can be processed.
If the machine temperature operates at ambient, make sure the machine heats up to a process temperature before attempting to extrude or inject plastic. The information is available from the Environmental, Health and Safety Committee. Water follows this information; this will minimize the amount of energy usage. If the machine will be down for an extended period of time, turn off the process heat for the barrel and unplug the machine from the power source. This is important in saving energy and ensuring safety in case someone mistakenly attempts to turn on the machine while it is not in operation. During the machine shut down scope, make note if there are any machine components that need repair or service. This will help to schedule an organized shutdown at a later time.
Start-up and Shutdown
First time starting up or after a long period of machine inactivity, it is advisable to manually rotate the extruder and increase the screw RPM speed to ensure no residual moisture is present in the material, preventing it from getting stuck and possibly damaging the barrel and screw. This step is particularly crucial for vented extruder systems.
Ensure the working area is clean and safe. Check and ensure there are no raw materials in the extruder/injection unit, which means the last job’s clean-out procedure was done thoroughly. Check and ensure all the control switches and buttons are in the “off” position. Check the hydraulic unit, if available, and ensure its fluid levels are sufficient. Turn on the main switch, wait for the machine to initialize, then turn on the temperature controllers. For recycling machines, the temperature controllers should be set at about 10-20 degrees lower than the melting temperature of the material to prevent unnecessary temperature heating and prolong the lifespan of heating elements and the screw. (e.g. The melting temperature of PP is 210-270°C, so the temperature setting should be around 200°C) Step 1: Warm up the extruder/injection unit.
Start-up Start-up procedures may vary according to different machine manufacturers, but all of them should strictly follow the machine operation manual, which should also be the basis for finalizing standard operating procedures. Following are some general standard operating procedures for starting up plastic recycling machines.
Material Handling
Flake materials can experience degradation and/or may have a wide range of bulk density. In these cases, a dense phase pneumatic conveying system can be utilized to minimize damage. This is a slower, more controlled conveying method and it uses a lower air pressure and a high material-to-air ratio. A well above the entry port on the storage silo allows for a vertical drop which, in some cases, can help minimize the distance required for horizontal conveying and prevent line plugs. An air filtration assembly with a small receiver drum can be located at the end of the convey line in order to reclaim conveying air, and there will be a short vertical leg coming off of the line with a sweep elbow. This allows for conveying of different materials in the same line by minimizing contamination between changeovers.
Material handling systems will depend greatly on the type of materials to be used. For plastic recycling, material will be in the form of washed flake or regrind, just conveyed into the storage silo. First, consider the regrind. This material is often bought in gaylord boxes and usually has some sort of contamination. In a typical system, a tool receiving hopper is used. It can be as basic as a feed hopper with an agitator and a slide gate. An agitator and/or vibratory pan feeder are located above the hopper and are used to provide positive force on the material to feed it into the rotor of the small. In some cases, the tool will be ground down into small flakes. This can be accomplished using a low-cost screen with the appropriate size, or the flakes can be produced from the beginning. This type of material can often be pneumatically conveyed into the storage silo.
Machine Maintenance
What tasks need to be performed and how often? The manufacturer of the recycling equipment often provides specific recommendations in the equipment manual. However, based on the type of equipment and the operating conditions, specific tasks and frequency may need to be customized. A comprehensive list of equipment and maintenance tasks to consider is provided, though it may not apply to all situations. This list may serve as a starting point for developing a specific maintenance plan.
Who will be responsible for the maintenance of the recycling equipment? Assigning a specific individual to be in charge of all equipment maintenance will increase the likelihood that the recycling equipment will be maintained properly. If maintenance tasks are simply added to existing operator position duties, it is unlikely that they will be performed consistently. Therefore, a new position primarily responsible for equipment maintenance is likely the best way to ensure that the investment made in recycling equipment will continue to pay off in the long term.
Quality Control
The first stage of quality control is material sorting. For recycling to be both economically viable and to meet reprocessor quality requirements, the material input to any recycling process should be sorted to a level where there is no more than 5% by weight of the incorrect polymer or polymer containing unacceptable levels of contamination. Any more than this and the material downgrade means that it cannot be used in the same application and this is where the recycling chain starts to break down, with recyclate being “down cycled” to inferior applications until it reaches the final stage of disposal. At each downgrade in application, there is a reduction in material value and an increase in competition. It is unrealistic to expect a good level of material sorting without the widespread use of a classification system for plastics which identifies both a resin code and a recyclability code. The current situation is that there are many plastic items which do not carry any form of plastic identification/recognition and this severely hinders automatic sorting systems. A related issue is the marketing of packaging as “recyclable”. If all plastic packaging was, in fact, recyclable, there would be no logical reason why it could not be identified as such, and this would significantly ease the sorting of post-consumer waste. Beyond identification, automatic sorting of plastics is currently achieved most effectively by a sink-float process usually carried out in water. This is useful where there is a large proportion of two different plastic types which have similar density. At a smaller scale, the most common form of sorting is by use of some form of near-infrared spectroscopy (NIR) system which provides a quick and easy method of identifying many plastic types and grades. In general, the above systems give a good indication of the current plastic sorting methods. Automatic methods are continually being refined as the industry works towards minimizing the cost of recycling.
Material Sorting
The next logical step in plastics recycling machines is to save costs by opting for a more efficient and therefore more expensive material for recycling instead of separating material post-recycling. With the high cost of manpower and the high level of contamination with current dry material feeders, Vits is on the market with a new generation of melt filtration systems, offering a vast improvement on existing models with its automatic screen changer RSFgenius. This will no doubt be beneficial in the future of plastics recycling. The most prevalent method of material sorting technology amongst plastics recycling machines is still the hydrocyclone. With little change in hydrocyclone design over the last decade. This is unfortunate, as hydrocyclone separation of mixed plastics is not always possible and if possible, the purity of the fractions inadequately meets the specifications for the end product to be of commercial value. This is due to the fact that specific gravity is often very similar between different kinds of plastics and/or there is a sizable contamination of paper or plastic labels. The common practice with current methods is to market a system to a waste management company and then allow the company to take and landfill cheapest fraction of material i.e. PET bottle plastic and keep the money from the sale of the other end product. This defeats the purpose of wanting to recycle all materials and is no longer viable in many parts of the world where the cost of landfill has become prohibitive, some systems no longer possible to market. Intensity rare earth magnetic separators are a new method that is more attractively approaching commercial viability. The basic design exploited the fact that plastic is a non-conductive material and therefore there is a degree of electrostatic charging. This charging leads to a magnetic moment which is induced when the material passes through a magnetic field. This moment will cause a force on the polymer which has a linear dependence on field strength, material susceptibility and the rate of change of field strength with distance. Traditional magnetic separators have been unsuccessful in separation of plastics due to the transition of all but the cheapest consumer items in recent years from thermoset to thermoplastic materials. During its research Caleffi from Italy found that there is a range of Curie temperatures of ferromagnetic materials and formed a new design of magnetic separator in which the magnetic field could be fully utilized in separation without raising the temperature of the plastics to the point of thermodegradation. The ferrous materials used in construction of machines for plastic processing can also be removed using this type of separator. Ecomation Oy, a Finnish company is aiming to develop an optical method based around near-infrared identification of polymers. This too offers promising new technology for material sorting.
Contaminant Detection
A two belt conveyor system is used to spread the material across the width of the conveyor, and then allows a monolayer of material to pass under the NIR camera and illumination module. The NIR camera images the material and produces a monochrome image based on the intensity of light in the NIR region, while the illumination module provides an image for colour identification. The monochrome image is then analysed to detect individual granules of the contaminants by the use of edge detection algorithms. Since the edges of contaminant granules are not clearly defined in the NIR image, the original image is transformed using a Sobel filter to enhance the edge definition. A watershed algorithm is then used to segment the granules, and various other algorithms are used to define the properties of these granules. A region of interest (ROI) is defined over each granule, and then this ROI is expanded to incorporate the surrounding area. A pattern recognition algorithm is used to match the granule against a template in a contaminant library. If a match is found, the location of the granule is marked and the ROI is filled to prevent further analysis of the same granule. The colour image is then analysed to see if the granule is the same colour as the surrounding material. If it is, the surrounding material will form the sink product, whereas if it is a different colour the granule and surrounding material will form two separate products. If the contaminant granules are spread out over the whole width of the conveyor, it is possible to adjust the separation system so that the purest reclaimed material is produced alongside one or both edges of the conveyor, and the contaminants are deposited in the central area and removed sorts as to minimise loss of quality of the reclaimed material. This is achieved by choosing the locations of the contaminant and product interfaces, and then using data from the image analysis to guide the position of a separation barrier. This method has the potential to dramatically improve the quality and cost efficiency of sink-float separation processes. Other work at WMPI has involved the use of similar NIR systems for detection and identification of contaminants in a German funded project to develop on-line quality control methods for the food industry, a system to detect PVC contaminants in scrap plastic material, and the development of an automated method of identification and removal of metal contaminants in a polymer processing extruder.
In plastic recycling, an important step in improving the quality of the processed reclaimed material has been the development of sensitive and efficient methods for on-line quality control to identify and remove contaminants. One such method, developed by WMPI, uses a near infrared (NIR) spectroscopic imaging system for automated detection and identification of contaminants (typically dark coloured plastics) in a sink-float separation process. A simplified diagram of the system is shown in Figure 5.2.
Output Assessment
The plastic recycling industry is proving to be a multifaceted space. In recycling of each post-consumer plastic bottle, process engineering must consider the physical, chemical, and toxicological characteristics of the bottle. The reason for this is simple – the attributes of the incoming material may have changed to a certain degree from its initial state. Because bottle grade resin is the most valuable resin in the PET, HDPE, and PP industries, it may be advantageous to upgrade the recycled stream to this level. Therefore, the best end-of-line strategy in recycling materials such as PET derived from post-consumer bottles is an analysis of the efficacy of removal of bottle label and cap colored inks, followed by a color sorting process which differentiates material into clear and non-clear resin. A similar logic can be applied to HDPE and PP recycling. Therefore, enhancement of recycled resin value can be achieved through one or a combination of these techniques in output assessments. Due to the fact that such process enhancement can add value in the plastic recycling stream, accurate determination of whether enhancement has actually been achieved is a critical facet in cost-benefit analysis of output assessment technologies. This may be the case where, at present, technologies offering impressive solutions are pushed into industry adoption when the algorithms are not yet optimized to provide worthwhile results. This type of progress assessment is generally classified as on-line quality control and is traditionally performed with off-line analytical techniques and statistical analysis of process capability. The cost of such quality assessment can vary largely, and the possible precision of resin property may depend on the demands of the plastic recycling industry. For specifications where a broad and forgiving definition of resin quality exists, a technique such as near-infrared analysis can be employed to provide a quick analysis of resin type. When resin type specification boundaries are quite close, it may be necessary to use a more sophisticated technique such as differential scanning calorimetry (DSC) to test for polymer thermal properties. DSC measures the energy input to a material as a function of temperature. On-line DSC is now available; however, it has not yet been employed for quality assessment in the plastic recycling industry.
Troubleshooting and Maintenance
Common issues Troubleshooting with extrusion equipment is typical, as the process involves many variables. Sometimes a process screw may produce too much or too little output. A number of things can affect this. The heater controls may fluctuate and cause temperature variation at the barrel zones, thus causing irregularities in the plastic melt. The screw itself may have wear from abrasives in the plastic. This wear will cause differences in output because the channel depth and the flight clearances will increase. A worn barrel will have the same effect. The screw rpm can slip on electrically driven machines. Lastly, it is important to make sure that the material being used has not been changed and that the proper drying procedures for that material have been followed. Often times the problem can be solved while referencing back to these points.
Common Issues
Measures to correct these issues include a change to higher quality, wear-resistant components, and reduction of screw speed and torque. It is possible to recover some worn components by reducing screw recovery and increasing barrel temperatures, but this is only a short-term solution and full recovery may not be possible.
High screw speed and torque with commodity plastics can cause screw and barrel components to wear quickly, and abrasive wear will result in increased screw slippage and reduction in output, often with occurrence of melt temperature surging. This will also be the case when using fillers or reinforcing agents. Screw slippage can also be caused by worn or damaged thrust bearings.
Common issues with extruders are also similar to most other processing machinery. These include fluctuations in operating torque and speed, inability to reach or maintain set operating conditions, and excessive screw or component wear. The root causes of these issues often stem from the material and the design of the screws and components. It is likely that your machine was running well when processing a different material.
Regular Maintenance Tasks
– Establish a weekly, monthly, and yearly maintenance schedule with daily checks to be performed by the machine operator. – Keep a comprehensive log of data on machine usage and faults to enable problems to be detected early. – Provide easy access and use of ergonomically designed tools to prevent many operators from neglecting minor maintenance tasks. – Train maintenance personnel according to the machine manufacturer’s recommendation. More intense training is recommended for larger and/or more complex machinery. – Scheduled machine downtime for maintenance may not be popular but is by far the most cost-effective method of maintenance in the long term. – Consider modifying machine or tool designs to improve ease of maintenance, eliminate awkward or dangerous tasks, and improve access for operators.
Maintenance of machines is vital to ensure efficient and economic operation. A poorly maintained machine will have a shorter life, have frequent breakdowns, and consume more energy. The following are some general recommendations for maintenance tasks that should be carried out on recycling equipment:
Safety Guidelines
It is essential that you follow the operating instructions of the supplier when using the machine. Guard or fencing removal and cleaning routines must be a part of the standard operating procedure of the machine. How often will depend on the rate of cleaning required. This is likely to be required on a less frequent basis, but it is essential that an LOTO procedure is devised specific to each individual machine cleaning operation. A risk assessment should be carried out for all tasks involving interaction with the machine that are identified as being hazardous. Workers must be competent and adequately trained to use the machine. This is a requirement as specified by the PUWER regulations. An adequate level of training will ensure that the machine is utilized in the correct manner and maintained to a satisfactory standard. Juice recommends that training should include an element of both theory and practical sessions, which will also be used to assess the competence of the trainee. This may involve some form of examination to test trainee knowledge. Always ensure that operators are aware of the location and operation of all relevant emergency stop buttons. An emergency procedure must be detailed for all tasks involving the use of the machine in the form of a job-specific risk assessment. It is important that the risk assessment is clear and easy to understand, ensuring that all hazards are identified and suitable method of risk elimination specified. Should any task be identified as having a high level of risk, a decision will need to be made as to whether it is essential to the task to proceed. Where possible, hazardous tasks should be avoided. Fall-back procedures must be put in place and a level of preparation made. This will include an assessment of what the possible emergency scenarios may be and how these can be resolved with minimum risk to the personnel involved. Measures to mitigate identified risks may include a modification of the machine or a temporary change in the working environment. Emergency procedures must be briefed to all involved personnel and it will be a requirement for all procedures to be both documented and regularly reviewed.
Personal Protective Equipment
The following recommendations are intended to be used as a guide for the type of PPE to be used in different recycling situations. It is imperative that the user conducts a thorough risk assessment to identify potential hazards and determine the exact type of PPE that is required. This is beyond the scope of this document, but the following information may be used as a reference for a PPE risk assessment.
Personal protective equipment (PPE) in the workplace should be considered secondary to engineering controls and safe work practices; nevertheless, its importance should not be underestimated. This is especially true in recycling operations where PPE can be a worker’s last line of defense. It is essential that the type of PPE prescribed is appropriate for the hazards faced in the job. Employers have a duty to provide PPE to employees and ensure its use. PPE must be properly maintained and of a prescribed standard. It is the responsibility of the employee to ensure they use the PPE as instructed in accordance with their training.
Emergency Procedures
It is also important to have a suitable first aid and/or fire fighting kit nearby. This will facilitate quick and efficient action in the event of an injury to personnel or in an attempt to save the machine from further damage.
For emergencies involving damage to the machine or something that is in or on the machine, quick action is vital in order to save the machine and surrounding equipment. In this case, hitting the emergency stop buttons located on the machine is not the best course of action, as this will not prevent further damage should the cause of the emergency still be engaged, i.e. the screw on an extruder or the injection ram on an injection molding machine. The best action in this case is to allow the machine to cycle itself to a safe state. This is particularly easy with injection molding and extrusion machines, as the cause of the emergency will still be engaged but the cycle can be easily stopped and the screw or ram can be reversed out. With this in mind, an emergency involving this type of machine should be stopped by isolating the electrical supply to the machine as soon as it is safe to do so.
In the event of an emergency, the immediate actions of the operator can prevent further injury or damage to the machine. There are two different kinds of emergencies: those that involve injury to personnel and those that do not. In the event of an injury to the operator or other personnel, switch off the machine by hitting the main isolator switch. This is a large red switch located on the electrical control cabinet. If possible, do not move the injured person until it is safe to do so without causing further injury. Persons not familiar with the circumstances of the injury should not interfere with any controls or the electrical supply to the machine until it is safe to do so.
Environmental Considerations
An in-depth understanding of the recycling process, the available options, and the potential environmental impacts is crucial in assessing the green credentials of plastic recycling. There has been little research published to date on the life cycle analysis of plastic recycling. Even the wider implications for the entire waste and resource management of plastic waste are little understood. It is crucial that recycling technologies are compared to the disposal alternative in order to set into context the relative implications for the environment. Life cycle analysis is a study that evaluates the environmental impacts of a product from its manufacture, through its use phase, and its “end of life” including disposal. Although in-depth analysis of individual recycling machines is beyond the scope of this report, the analysis of the wider context into which the machines are placed is crucial in understanding the green credentials of recycling.
Waste Management
At the end of the machinery’s service life, the equipment itself is waste to be managed. Careful planning in equipment design can make disassembly and separation of materials easier. This will make recycling and/or reusing the materials more feasible. Bonded materials or mixed plastics and non-plastics should be avoided where possible. Due to the materials involved, the longest-lasting and most durable equipment is not always the best choice from an environmental standpoint. If a plastics recycling system can be made into a functional disposable product, the environmental opportunity cost may be lower. And finally, the most environmentally friendly way to deal with equipment waste is to have planned obsolescence and a replacement plan.
Various waste management options can be implemented during and after the service life of a plastics recycling system. During the service life of the machinery, waste reduction can be achieved primarily through process modification. Recycling of waste plastics inevitably creates some unusable material. Generally speaking, minimizing the number of processing steps and maximizing the amorphous regrind output will keep post-processing to a minimum. Optimization of the processing conditions to produce a cleaner and more pure regrind will also reduce waste. If foreign plastics or materials can be sorted from the input material before it enters the recycling stream, this will greatly reduce the amount of waste created. Due to the high cost of waste plastics, many recycling system processors are very reluctant to dispose of any material. This often leads to the accumulation of waste material, which should be kept to a manageable amount. If a reprocessing objective can’t be met, a decision to sell the waste material for use in an application not possible with the current system can be made. In some cases, it may be possible to use the waste material as feedstock for another recycling system. An option of last resort for post-processing waste may be landfilling or incineration. If waste material must be disposed of, incineration provides a more environmentally benign alternative to landfilling due to the pollution associated with burning hydrocarbons being spread out over the entire earth in the form of CO2. Landfilling tubs of liquid waste is a waste minimization option to reduce the amount of waste material that must be incinerated or landfilled. Any waste plastic from a recycling system can be chopped or melted and entered into the plastics industry’s wide-scale recovery system often called “back to resin” processing. Any waste reduction that cannot be avoided should, at the very least, be disposed of in an environmentally responsible manner.
Emissions Control
The primary environmental considerations in the use of plastics recycling machines centre on waste management and emissions control. Although such machines are designed to produce as little waste as possible, undesirable by-products such as discarded contaminated waste and cleaning chemicals are often produced. The waste management of such materials will usually be the same as the recycling of the plastic material being processed. Emissions control involves the monitoring and control of air and water emissions. Air emissions are primarily in the form of volatile organic compounds produced during the extrusion and manufacture of plastic sheet or moulded plastic products. Incineration and thermal oxidation are widely used methods of emissions control, and one supplier of emissions control equipment to the plastics industry is considering developing a system specifically for the control of VOCs from plastic manufacturing processes. Monitoring and control of water emissions is important if the plastic recycling machine is cleaning, washing, or using solvents to eliminate contaminants from the plastic material. For instance, using detergents and solvents to clean and remove paper labels, dirt, or adhesive from PET bottles in a sink float system will produce wastes requiring treatment, with water often being used in the process. Such contamination of wastewater in plastic washing processes can be difficult to detect, with the waste not necessarily being a different color than the clean water. A cost-effective method of monitoring water emissions is to measure the Biochemical Oxygen Demand (BOD) and TOC levels of the wastewater. Although BOD levels can be tested and controlled with a simple water treatment system, detecting the different contaminants to determine the specific treatment the wastes require can be difficult.
Cost Analysis
The first method used for the recycling of waste plastics to form a useful product is the Messmer Plan. Due to the low cost of implementation, unskilled workers, and low energy input, the investment is not high. Injection and compression molding are used to form the products, but due to the constraints of these processes, the scope is limited to simple non-durable products and it is not possible to reform a vegetable rack or milk crate to their original standard. A cost analysis of the entire process has not been conducted due to the variable cost of labor and energy.
It is important to determine the costs involved in implementing a recycling idea. This will determine whether the comprehensive recommendations are practical. The initial investment in support of the ongoing statements on the recycling of waste plastics to useful products.
Initial Investment
Initial investment covers all the expenses when a company decides to open or start a project to ensure the project can run smoothly. Full preparation must be done with careful planning on initial investment. Initial investment can be categorized into a few items such as the cost of investment for the project, operating capital, and additional investment. The cost of investment for the project is one of the biggest expenses when a company decides to implement or start a new project. It is the amount of money that is used to actually start the project. In terms of purchasing the plastic recycling machine, the cost can differ depending on the technology and types of machines that the company wants to purchase. Usually, to purchase high technology machines, the cost will be higher compared to purchasing lower technology machines. But high technology machines are more efficient for operators compared to lower technology machines. The machines can produce high-quality recycled plastic products. The basic types of plastic recycling machines usually cost around $1000-$50000. The machines are cheaper compared to complex and high technology machines. High technology machines use Pro-Sort, Optical, and color plastic specific systems. This system is more advanced compared to traditional systems that can differentiate plastics based on resin type. The price difference between PET (CR-1100-PET) and PP (CR-1250) is $175,000 – $200,000 for Resin Sort Systems. Although both technologies are functional, the higher-priced machine is more efficient and profitable. Operating capital is used when the company buys and operates the machine until it produces the recycled plastic product. The operating capital is expended for a certain period. This capital is used to finance the ongoing cost of operation. Ongoing operation costs include labor costs, costs of repairs and maintenance of machinery, and utility usage charges such as electricity, water, and telephone. These costs are incurred as the cost to produce recycled plastics. Additional investment is an investment made by the company after a project is completed. This investment is for expanding or adding more features to the existing project to make it more efficient and productive. It can be an additional investment in buying new technology for recycling machines, hiring more workers, or finding a new location to expand the project.
Operational Expenses
Step recycling equipment can also be simply evaluated in that the cost per pound of finished product can be added to the product output rates. This sort of equipment is often forgotten in that it can generate high costs due to having much longer processing times compared to an extruder. Providing a specific explanation of expenses to the customer is often wise, as this will help in promoting the long-term use of equipment and ensure customer loyalty. Step machine designs can also factor in expected product rate increases with minimal expenses by converting to a larger size machine. This type of scenario can be shown with a separate evaluation comparing expenses using only one machine compared to a higher product rate using future machine purchases.
Extruder type recycling equipment is fairly simple to evaluate in terms of operational expenses since the cost of hourly operation can be precisely determined through the use of a power purchase agreement. Since power purchase agreements have fixed costs for the life of the equipment, current expenses are added and divided by the number of hours of usage to find the cost per hour. This cost can then be multiplied by the yearly operating hours plus a small amount of money for maintenance costs. The expected equipment life can also be factored in to determine the cost per pound of electricity. When considering equipment, it is often desirable to compare the cost benefits of using a direct drive machine compared to a belt-driven machine using a large reduction motor.
Every recycling equipment manufacturer should thoroughly evaluate operational expenses when making an offer to customers. This is often more important to the customer than the cost benefits of making a higher priced initial equipment purchase. Unfortunately, operational expenses are relatively easy to come by due to the fact that they are based on real costs, while cost benefits are often speculation based on future market conditions. To accurately evaluate expenses, there are two basic scenarios that should be considered. One is the expenses to operate equipment at the current processing rate, and the other is the expenses based on a projected processing rate. The projected rate will often require more equipment than is currently needed, so it’s important when evaluating expenses to distinguish between the two.
Future Developments
The final method is the development of new recycling plastics. This method is usually the result of new plastics being developed, as mentioned earlier, and the transition to using better recycling plastics and new recycling methods for that plastic.
An alternative to increasing the quality of recycled plastics is the method of testing new recycling plastics with various methods with the hope to discover the best recycling method for a specific type of plastic. This is another ideal opening as there are new plastics being developed every day with no knowledge of the best method to recycle that plastic. The method the Proto 6 has endeavored to test various recycling methods, so it’s a method that can be an example for possible future developments.
In efforts to make plastics cleaner and recycled plastics, it’s beneficial to be compatible with future technology methods. An example of this method and a way of cleaning recycling plastics is the use of ionic liquids. Ionic liquids are solvents that can dissolve polymers by forming a special type of liquid in which, if a polymer is submerged into the liquid, it will break up into its constituent monomers. A machine that can create a better form of recycling and a cleaner recycling plastic method would be a modified shredder/extrusion machine with very low emissions of volatile organic compounds. This machine is typical of what is available in the present day, so when it comes to providing cleaner plastics, the method has not yet been developed. This is an ideal opening for providing a new method to clean recycling plastics.
An alternative to increasing the rate of recycling would be the development of an energy-efficient machine that is capable of various recycling methods. This idea aligns with the steadily increasing development of renewable energy and its desired implementation on a global scale. A machine that utilizes green energy sources is somewhat a reality with the surplus and low energy requirements of the Proto 6. Steps to make the Proto 6 completely energy self-reliant with the use of solar energy would potentially create an alternative form of recycling some decades in the future. Steps towards green energy are also beneficial to increase the quality of recycled plastics.
To increase the rate of recycling, one ideal development would be to create a higher capacity version of the Proto 6 with the ability to produce a 24-hour day’s worth of plastic recycling. This would allow the Proto 6 to compete with current-day large-scale shredding and extrusion machines that have high output rates, with a method that can provide cleaner recycling and produce a sizable income. High output rates are sought after in today’s society and are often the reason why the purest forms of recycling are overlooked. Creating a higher capacity Proto 6 would provide an alternative method of high output rate recycling that is clean and eco-friendly.
This research has led to the development of two concepts for future recycling machines, which are technology advancements and following industry trends that aim to increase the rate of plastic recycling to help preserve the environment. These concepts hope to be a catalyst in creating global sustainability. Technology advancements in the recycling machine may not be a necessity to recycle plastic, but its implementation should not be forgotten. Technological advancements in recycling machines should aim to increase the rate of recycling and/or the quality of the recycled plastic.
Technological Advancements
The most promising of these technological advancements is development in the area of feedstock recycling. The aim is to copy the process of cracking crude oil in a fluidized bed catalytic reactor to produce basic hydrocarbons that can be used to make new plastic. This is the first feasible method to recycle mixed or heavily soiled plastics, but there are still many years of research and development before this technology will be implemented on a commercial scale.
Initial work has been done in the area of process control using logic to switch between barrels on an extruder to maintain a set product temperature and viscosity. More recent efforts involve the development of intelligent screws that will alter the energy put into the plastic depending on pressure readings and maintain a constant melt temperature using various zones and a cooling system.
Development in technology encompasses many broad areas, such as intelligent processing, increased efficiency and effectiveness of processes, process control, material identification and sorting, higher product quality, and increased equipment life. There are many processing machines in operation that have been in service for 25 to 30 years and still produce acceptable product. However, with the state of the industry today and the implementation of tighter quality control, longer service life of equipment, and sustainable manufacturing, this machine is not acceptable if it uses excessive energy, produces off-spec product, and has a negative environmental impact.
Industry Trends
The market demand increase will be driven by today’s post-consumer plastics material recovery programs. According to the American Plastics Council, post-consumer plastics collection has increased steadily over the last two decades with an average annual rate of 63% since 1990. This figure reached 1.4 billion pounds in 1999 and it is expected to increase dramatically with new pledges by companies such as Coca-Cola, Nike, and Procter & Gamble to use recycled materials in their products. The increased demand will also be met by exports to China and other countries in Asia where infrastructure for the manufacture and collection of recycled materials still lags behind North America and Europe. In order to continue competing with cheap virgin material manufacturing in these regions, today’s North American and European compounders must produce high quality wide-spec materials at low costs from low-cost feedstock. This will be accomplished by new plastic recycling machines and process additive equipment to reduce production costs, and also by improved scrap material logistics to increase the utilization of recycled materials. An example of such industry activity to develop new wide-spec materials and increase utilization can be seen in the new initiatives by the North American automotive industry. High global competition and oil prices have led to these initiatives to lighten vehicles with plastics and increase usage of recycled materials, where cost savings will be directed to higher R&D investment and reinvestment in new plastic parts production.
It is clear from figures from the Society of the Plastics Industry, for example, that the dominant market for a particular plastic recycling machine configuration consisting of a specific combination of all machine functions, the baseline configuration, will not be sufficient to meet future market demand. This configuration has been the baseline production system for near prime materials (which represents roughly 80 percent of the plastics market) in the past. Though the configuration will continue to play an important role in meeting the projected rise in demand for near prime materials, increased efficiency will be required to free capacity for the production of wide-spec materials to meet the increased demand without drastically reducing the price of near prime materials due to an oversupply. High efficiency recycling machines suitable for near prime production as well as wide-spec will also be considered for purchase to replace existing machines of the same function to reduce energy consumption. Finally, total production system combinations of new recycling machines and an increased number of process additive equipment will also be considered to introduce new innovative wide-spec materials to the market and maximize the compounder profitability from post-consumer or post-industrial recycling.
