Selecting a thermal reclaimer for green sand. (Guidelines for selecting a reclaimer, part 2).
Having discussed several types of equipment used in green sand reclamation and how they and their ancillary equipment function in part one last month, here are some system guidelines that will be of assistance in developing and selecting ing a system:
* preliminary testing;
* continuous, unattended operation;
* system consistency;
* process controls;
* dust collection;
* ample storage strategically located;
* space availability;
* economic justification.
It may seem odd, in using basically similar sands, bentonites, carbon additives and a variety of core resins, that such vastly different base materials can be candidates for reclamation, but this is often the consequence.
Therefore, the most important first step toward thermal reclamation of green sand is to have sand tested using a representative foundry sample. These tests will provide a base line for further system design and selection. They will also provide economic justification for necessary future equipment purchases required to reclaim and process sand. It is well to note here that the system must be designed to work with the test sand and reasonable variations of it.
The tests should not only supply qualitative data, but also quantitative data that will establish the capacity requirements by determining the expected reclaim efficiency (the ratio between net usable sand and the gross input sand). This is extremely important because reclaim systems in general are rated by their throughput capacity and not by their output capacity.
The output of the reclaimer can be further reduced if dust collection and exhaust hood designs are improper. These two factors could cause losses as high as 20-30%; thus, sizing a reclaim system simply on the basis of new sand requirements is not recommended because that value will result in a shortfall of capacity equal to the reclaim system losses. A more prudent rule would be to use the greater of:
* 1.4 times the current new sand additions;
* the net amount of required reclaim sand divided by actual tested efficiency.
As an example, if a system now requires two tons of new sand per hour, and tests show reclaimer losses of 17% with 5% new sand additions required to make quality cores, there claimer should be sized for between 2.4 and 2.29 tons per hour (tph).
All thermal reclaim systems are costly in terms of price per unit capacity. Therefore, it makes sense to design these systems for continuous operation (up to 20-24 hours a day, six days a week). This provides for maximum system utilization and, at the same time, keeps its amortized cost per ton of sand to a minimum. Naturally, this type of operation will place a premium on rugged, heavy duty construction to assure greater system reliability.
A process flow model made at the beginning of the project will guide the selection and sizing of the equipment preceding and following the reclaimer. This allows the reclaim system to be tailored to actual plant operations including such variations as large influxes of scrap cores, floorsweepings and floor mold shakeouts without interrupting operations.
Automated control systems should be designed to sustain continuous operations with only routine preventive maintenance, inspections and cleanup. This will reduce the cost per reclaimed ton of sand and further justify the economics of the system. Again, a carefully prepared process model at the beginning of the project will assist in designing a system that can operate unattended.
Although a typical thermal reclamation system is a collection of proven components, variations in the quantity and the physical and chemical makeup of the incoming sand can have a dramatic effect upon the equipment operation, fuel-air requirements, combustion, dust collection and the quality of the final product.
If the incoming sand varies widely in physical and chemical make-up, it may be prudent to store different sands-separately, feeding them into the reclaimer in a consistent blend. This would apply for lump sizing because lumps can cause feed and processing problems.
The most critical element in a thermal reclaimer is the requirement to provide verifiable and consistent temperature control throughout the calcination process. This will ensure maximum removal of organics and breakdown of the bond while not exceeding the fusion temperature. Equipment and controls selection is the key to ensuring this consistency.
Dust collection will also have an interacting effect on the success of the system, and it is important that the dust collector for the reclaimer be a dedicated unit. The reclaim system should never be connected with other systems if they are prone to wide variations in volume and pressure drops because the more variations allowed in the system, the more variations in the output.
The capabilities of today's control systems are well-known and provide an excellent opportunity for thermal reclaim system design.
State-of-the-art motor controls and programmable controllers can easily provide the capability for unattended operation. They can provide system diagnostics able to detect faults, thus minimizing trouble-shooting and downtime. Unattended systems should be equipped with automatic shutdown circuitry to provide protection in the event of a critical component failure or system fault.
These controls can provide the data logging capability for either direct monitoring and review or have data processed through the plants mainframe or network computer system.
In sum, the controls for a thermal reclaim system should be selected on the merits of their ability to provide process consistency and stability, affect overall system reliability, process data, and possess the diagnostics to detect faults and minimum downtime.
Dust collection cannot be treated as an after thought, but rather, it must be recognized as an integral part of the system. As previously stated, the ideal situation is to have a dedicated dust collector for the reclaim system. Should an existing collector have the capability to work in the system, it's shared operation should be such that it will not impose volume or pressure drop variations on the reclaim system.
If such variations exist, they must be either equalized by the addition of control dampers, etc., or otherwise eliminated, or a dedicated collector must be used for the reclaimer. External variations in the dust collection system can cause the following problems:
* inadequate removal of unwanted fines, dead clay, ash, etc.;
* excessive removal of usable sand grains;
* imbalance in the recuperator-preheat system, which can unduly tax the temperature controls;
* excessive duct work wear;
* excessive dust accumulation causing housekeeping problems and potential component contamination and failure.
Basic hood and ductwork design must optimize both the removal of unwanted fines and the retention of usable sand grains. Storage Location
As noted, the reclaim system should be designed for continuous operation even though the plant may operate only one or two shifts.
Adequate storage of the incoming spents-and and outgoing reclaimeds-and is one of the least costly means of optimizing the system. The added expense of additional storage is minor when compared to the operational utility that extra storage can provide.
Buffer storage areas can provide a more consistent reclaim operation, assuring that critical system components, such as the preheater, calciner and post-scrubbing equipment, will not be stopped or operated at reduced throughput.
Buildings play an important role in the success of a reclaim system. While it is more desirable to select the equipment arid plan a building or penthouse around it, economics will not always permit this luxury.
Therefore, if plant space is available, it may be more economical to select equipment based on availability. Space considerations may favor the rotary kiln or fluid bed separators for low overhead, greater floor space situations, or the taller integrated fluid bed or fluid bed separators where more headroom but less floor space are available.
Another consideration is to place the reclaimer in a distant location and bear the cost of conveying the sand longer distances. Careful site selection is important because conveying systems serving multiple destinations with capacities of 20-25 tph or less will favor pneumatic transporting, while fewer destinations and greater capacity will favor belt conveyors. in either case, investment in a relatively low operating cost building should be carefully contrasted with the higher cost of materials handling equipment.
If adverse weather conditions exist, heat exchangers in the reclaim system may be a cost-effective consideration as a system component.
Failure to establish economic justification for proper system design and selection guidelines can result in disastrous results. Careful consideration of the aforementioned seven guidelines will provide system parameters that will be accurate and economically defensible.
If a proper reclaim system cannot be justified, a poor selection may prove a worse investment than none at all. With the variety and quality of equipment available today, coupled with the ever-increasing cost of new sand, transport and disposal, the latter case should not prevail.
Water Quality & Waste Disposal Committee 10-F
This article provides a preliminary view of the issues surrounding the reauthorization of the Resource Conservation and Recove Act (RCRA). The act governs the management of solid and hazardous waste in the U.S. and could have significant impacts on foundries and other U.S. manufacturing industries.
Potential impacts on foundries include stringent and costly recycling process controls and increased disposal costs due to an increase in the amount of foundry materials considered hazardous. Highlights of the major issues and proposed legislation are provided as are environmental community and industry positions on RCRA. A proposed strategy for improving the act from a foundry industry perspective is also provided.
RCRA was initially passed by the U.S. Congress in 1976. Subtitle D of the act addressed the management of solid waste." Subtitle C of RCRA established a "cradle tO grave" hazardous waste management system and required the U.S. Environmental Protection Agency (EPA) to adopt regulations to implement the intent of the law. RCRA allowed states to develop their own solid and hazardous waste management programs, as long as they called for standards that were as stringent as those outlined under the federal regulatory program. Subsequent EPA regulations defined the terms 'solid' and 'hazardous' wastes and devised standards for the management of each.
RCRA was amended in 1980 and again in 1984. The 1984 Hazardous and Solid Waste Amendments (HSWA) have had a significant impact on U.S. industries, including foundries. Major EPA rules issued under HSWA include land disposal restrictions that now require all hazardous waste to be treated to "Best Demonstrated Available Technology" standards before being disposed of in a landfill.
The Toxicity Characteristic Leaching Procedure TCLP) test replaced a former test method in September 1990. TCLP is used to determine if a solid waste is considered hazardous based on its ability to leach certain constituents under acid conditions. This test is generally more aggressive on metallic waste streams and has greatly increased the amount of materials considered to be hazardous waste, particularly impacting nonferrous foundries. EPA expected the TCLP rule to triple the amount of waste considered hazardous under RCRA.
In July 1990, EPA outlined the structure of the HSWA corrective action program in a proposed rule. This program would impose site investigation, study procedures and cleanup requirements for RCRA facility owner/operators. The complexity of the proposed rule is probably best measured by the time necessary for EPA to develop a final rule in response to public comments. The final rule is not expected until January 1993.
Reauthorization of RCRA is now being considered by Congress. Walt Kiplinger, AFS vice president government affairs, expects floor action on the bill in 1993 or 1994. Although the
RCRA debate is in its preliminary stages, the following general topics appear to be the major issues being contemplated by
Recycling Management Standards-Placing control measures on industrial material recycling processes.
Definition of Solid Waste-New definition of solid waste, a key term with man policy implications under-both the solid and hazardous-waste management programs, would have costly effects.
Waste Minimization ProgramsWould require hazardous waste generators to prepare, certify and submit to EPA toxics used and source reduction plans-and performance reports. Requirements would be legally enforceable.
State Issues-Interstate transport and disposal of waste has been a hot topic in Washington. Alabama and several other states have placed shipment bans on waste transported from states that do not have adequate disposal capacity assurance plans. In addition, states have used their authority under RCRA to develop regulations that are more stringent than federal requirements for industrial orphan waste," materials classified in the abyss between solid and hazardous waste. This has led to a gamut of regulatory approaches that have begun to impact fair competition and influence business siting decisions.
Several bills have been introduced in the Senate to address RCRA reauthorization. The most prominent bill, S. 976, was introduced by Sen. Max Baucus DMT) on April 25,1991 (102nd Congress, first session). The Baucus bill focuses on solid waste management issues, specifying recycled content standards for various recyclable commodities, packaging standards and national waste management policy goals.
The bill establishes a new class of materials under RCRA referred to as "hazardous secondary material" and requires EPA to "...promulgate requirements for the recycling, recovery and reuse of hazardous waste and hazardous secondary material..." Unfortunately, if EPA fails to issue these regulations within 24 months of enactment, hazardous secondary material" will be deemed hazardous waste and will become subject to all of the costly management requirements with which foundries are all too familiar.
It is likely that many foundry process residuals such as sands and slag would be classified as "hazardous secondary material" under S.
976. In addition, the bill requires that the EPA regulations covering the recycling, recovery and reuse of hazardous secondary material must contain:
* management standards essentially
* equivalent to hazardous waste requirements; corrective action;
* management of slag' in accordance
* with hazardous waste requirements
* if the slag is characteristically hazardous or derived from a listed hazardous waste;
* permitting, financial assurance and periodic inspection requirements. it is interesting to note that while the Baucus bill establishes recycling as the second-highest priority waste management alternative in the bill's national policy statement, it also poses onerous and costly requirements on businesses that practice recycling. It also removes the incentive from firms that practice this beneficial resource recovery technique.
S.982, a bill introduced by Sen. John Chafee (R-RI), expands on the recycling provisions contained in the Baucus bill. Chafee's bill is intended to 'clarify the Environmental Protection Agency's authority to regulate hazardous waste recycling..." The bill contains many troubling provisions, and could, for the first time, inflict RCRA requirements on industrial manufacturing processes.
The bill would essentially require recycling facilities to comply with the treatment, storage and disposal facility requirements set forth at 40 CFR 264 and 265 (as well as 40 CFR 266, 268) The Code of Federal Regulations (CFR) is a codification of general and permanent rules published in the Federal Register.
Chafee's bill would also require facility owner/operators using a "closed loop manufacturing process" or direct reuse manufacturing process' to provide certification to EPA that they are exempt from the costly recycling standards contained in S. 982. It is highly likely that foundries that reclaim sand prior to reuse would be subject to the costly provisions of Chafee's bill. Fortunately, passage of S. 982 appears unlikely.
Another bill was expected to be introduced in the Senate at press time and could not be reviewed before the publication deadline. This bill is to be sponsored by the Business Recycling Coalition (BRC), a group of several major industries, including AFS, and headed by the U.S. Chamber of Commerce. The bill will most likely be introduced by Sen. John Warner (R-VA). The BRC-Warner bill will probably propose a separate subtitle for recycling activities.
This "Subtitle K" approach will be based on the BRC statement of principles, which recognize that materials recycling is not waste treatment or disposal. The BRC advocates a recycling policy that recognizes the benefits of this practice and petitions Congress to establish a regulatory regime that encourages materials recycling, recognizing that recycling ranks high as a preferred strategy for pollution prevention.
Under Subtitle K, secondary materials would not be regulated as solid or hazardous waste but would be subject to existing environmental protection requirements such as Clean Air Act and Clean WaterAct emission and discharge limitations. In addition, recyclers would need to complete various record-keeping tasks to ensure compliance with Subtitle K. This approach balances the need for recycling controls with the tremendous environmental and economic benefits that this resource recovery practice provides.
An important bill is expected to be introduced this fall by U.S. Rep. Al Swift (D-WA), who heads the Subcommittee on Transportation and Hazardous Materials of the House Energy and Commerce Committee. The bill is expected to be a flagship of the RCRA reauthorization debate.
Two major environmental coalitions have announced positions on RCRA reauthorization.1
One group, consisting of 12 organizations including the Environmental Defense Fund, National Resource Defense Council and the Sierra Club, has prepared an RCRA position paper. The paper includes two points of interest to the foundry industry:
* mandatory recycling provisions for solid waste commodities;
* a mandatory reuse program for all vendors of large appliances and motor vehicles to enhance recovery and reuse of metals.
The War on Waste' is a coalition of more than 400 groups primarily coordinated by Clean Water Action and Greenpeace. The War on Waste platform calls for:
* a moratorium on the construction of hazardous waste landfills, incinerators, deep well injection and medical incinerators;
* a 50% reduction in the use of toxic chemicals by industry and a 75% recycling rate of municipal solid waste by the year 2000;
* an expansion of Subtitle C that would increase the amount of material considered to be hazardous waste.
Strategies for achieving these ambitious goals are not clearly identified in the War on Waste platform.
It appears that the position of environmental groups on RCRA reauthorization is somewhat divided and will probably change as various legislative approaches are considered by Congress.
Though the RCRA debate is in the early stages, several major issues that could impact the foundry industry have been identified. Preliminary positions on these issues are outlined in this section and may be changed as various policy options are put forth.
Recycling-AFS has aligned itself with the BRC. The BRC proposal should keep most industrial recycling processes and materials out of the complex and expensive RCRA management scheme. The Subtitle K program provides for control and management of recycling activities yet does not place the onerous treatment, storage and disposal facility requirements on businesses employing this environmentally beneficial practice.
This regulatory scheme is consistent with EPA's pollution prevention policy and the national waste management policy statements contained in other proposed RCRA legislation. The BRC proposal will encourage well-managed recycling processing at industrial facilities and will put the resource conservation and recovery theme back into RCRA.
Beneficial Reuse-AFS will press for recognition of foundry sand as a 'recycled or reused material" and will encourage management of this material under a regulatory program, but not under Subtitle C of the act. Individual states must consider recycling before treatment or disposal options for foundry sand and other similar industrial materials. Such action would be consistent with EPA's pollution prevention strategy.
Subtitle C Expansion-Expansion of this subtitle poses grave consequences for foundries and other U.S. industries. The TCLP rule has greatly increased the amount of materials considered as hazardous wastes. Expansion of Subtitle C would pose serious capacity questions (e.g., Could the U.S. waste management industry handle the increased volume of materials at a time when expansion of waste management facilities is literally impossible due to permitting and siting constraints?). The current business climate, combined with higher operating costs stemming from expansion of Subtitle C, could be detrimental to the U.S. manufacturing sector in the competitive international marketplace. Subtitle C expansion would be extremely costly and would provide limited environmental benefits and, therefore, should not be included in any RCRA reauthorization package.
Members of the AFS 10-F Committee are working closely with the AFS Washington office to follow the RCRA reauthorization process and provide technical support to Kiplinger. A position paper will be developed by the 10F Committee.
Our objective, once armed with a position paper and industry waste data, is to establish in RCRA the authorization for a flexible program to encourage the reuse of foundry sand, possibly subject to 'recycled or reuse material" regulations but not subject to the requirements of RCRA Subtitle C (hazardous waste). Such provisions would be consistent with the intent of EPA's proposed Pollution Prevention Policy Statement that calls for the full use of source reduction techniques and environmentally sound recycling and reuse.
A three-track political strategy to educate both the House Subcommittee on Transportation and Hazardous Materials and the Senate Subcommittee on Environmental Protection for this purpose is being developed.
* Track One would entail the development of an educational/public relations "kit" to include information and data on the industry, its customers, its importance to the economy and its waste disposal practices.
* Track Two would involve identification of relationships between AFS members as constituents of those subcommittee members and others considering RCRA reauthorization. The 10-F committee will inform state and local AFS chapters of RCRA issues during the reauthorization process through modern casting and Control News publications, Special Letter alerts, and AFS environmental conferences.
* Track Three would involve a commitment from these foundrymen constituents to visit (in Washington and/ or district offices) those RCRA-involved subcommittees and committee members and their staffs to promote" foundry sand as a recyclable, beneficial and useful material.
We think the evidence will be on our side, but we will have to tell our story aggressively if we want legislative recognition.
Beneficial reuse has been going on successfully for many years, and some documentation of that success has been developed. It is, however a relatively new consideration for the states and a new concept to most of the public.
We feel sure that inclusion of foundry sand in a new federal RCRA law would overcome much of the hesitation by state authorities to approve sand for
like all U.S. industries, foundries have a lot at stake in the outcome of RCRA reauthorization. The following actions are suggested for foundrymen who want to take a proactive role in the RCRA debate:
* stay informed of developments through your local AFS chapter;
* obtain the industry position paper when it is available;
* evaluate the impact on your business; establish or rekindle relationships with elected representatives and keep the AFS Washington office apprised of your efforts.
* get out the message! Inform your members of Congress of the RCRA issue, the industry position and its impact on your business.
The AFS 10-F Committee will continue to monitor RCRA reauthorization developments and keep the industry informed through various channels.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||Special Report: Sand Reclamation|
|Author:||Smith, Robert J.|
|Date:||Sep 1, 1991|
|Previous Article:||Detecting radioactive materials in scrap.|
|Next Article:||Many serious issues surround the RCRA reauthorization.|