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Section 7 REQUIREMENTS FOR DESIGN, INSTALLATION, AND ACCEPTANCE OF PNEUMATIC DUST-CONTROL SYSTEMS Section 1 of this manual pointed out that many pneumatic dust-collection systems in grain elevators do not perform as anticipated when they were installed. A pneumatic system should do two jobs; it should satisfy dust-emission regulations related to the environment and to occupational safety and health; and it should minimize the hazard of grain-dust explosions. Many installations do neither of these jobs. Sometimes, in fact, by building a false sense of security, they actually increase the hazard of explosions. This section proposes measures designed to correct this state of affairs on an industrywide basis. Pneumatic dust-collection systems may not perform as expected for several reasons. A major reason, however, is that the contractors who design and install the systems often are poorly qualified for the work. Grain elevators pose special requirements for such systems. These requirements are unlikely to be met by designers and installers who are qualified mainly in heating and air conditioning and in sheet-metal work. Yet elevator operators regularly have relied on contractors so qualified. Neither operators nor contractors can really be blamed for this situation. There have been no carefully developed standards of performance for pneumatic systems in grain elevators. Moreover, the special problems posed by these systems have not been widely publicized in the industry. Some such problems, in fact, have only recently become evident. Thus elevator operators have not known what performance to expect of their dust-collection systems. Similarly, many contractors have been unaware of the problems in design and installation that they must solve. The simplest approach to the overall problem would be for the grain industry to specify clearly what it needs in the design and installation of pneumatic dust-collection systems. This task might well be undertaken by one of the industry's trade or technical associations. Likely candidates are the National Grain and Feed Association (NGFA) and the Grain Elevator and Processing Society (GEAPS). Measures that the appropriate trade or technical association could develop include qualifications for contractors and detailed procedures for specification and acceptance of dust-collection systems. These measures are spelled out in the remainder of this section. 73
74 Qualifications for Designers and Installers A formal, industrywide procedure is proposed here for qualifying contractors to design and update pneumatic dust-collection systems for grain elevators. The procedure would be implemented by an appropriate organization acceptable to the industry. The proposed procedure follows; A. A permanent, five-member committee shall meet four times each year to compile and update an approved list of designers and installers of dust-collection systems for grain elevators. The committee shall be made up of; 1 Engineer who is actively employed in the grain or an associated industry, is familiar with dust-control design, and is aware of the needs of the grain industry. 1 Operating superintendent. 1 Fire underwriter. 2 Members-at-large. Members shall serve for two years. Three of them shall be appointed in odd-numbered years and two in even-numbered years by majority vote of the Board of Directors of the sponsoring organization. This committee should be assigned the primary authority and responsibility for selecting designers and installers who are qualified to meet the needs of the grain industry. B. Applicants for the approved list of installers shall meet the following criteria; 1. Contractor shall apply to the committee by letter 30 days before a quarterly meeting. Application shall include completion of a document developed for the purpose and generally resembling the Contractor's Qualification Statement of the American Institute of Architects (see Appendix B). 2. Contractor shall provide proof of bonding capacity. 3. Contractor shall provide a current Certificate of Insurance. 4. Contractor shall demonstrate a working knowledge of the guidelines in this manual or of any improved techniques that may be developed in the future. The application, in addition to providing sufficient information to identify the contractor, shall include the following; 1. List of dust-control jobs contracted during the past five years. 2. Names of employees who have successfully completed the Advanced Course of the Industrial Ventilation Conference. 3. Description of shop facilities.
75 C. Applications for the approved list of design engineers shall meet the following criteria; 1. Designer shall apply to the committee by letter 30 days before a quarterly meeting. 2. Designer shall demonstrate a working knowledge of the guidelines in this manual or of any improved techniques that may be developed in the future. The application, in addition to providing sufficient information to identify the designer, shall include the following; 1. List of dust-collection systems designed for grain elevators. 2. Name of employee last completing the Advanced Course of the Industrial Ventilation Conference given under the auspices of the American Conference of Governmental Industrial Hygienists, and date of completion. 3. List of engineering qualifications and description of expertise. Summary of Intent The foregoing procedure is proposed as a means by which the grain industry can improve the quality and performance of the dust-collection systems that it buys. The procedure no doubt would introduce a degree of regimentation and standardization. However, it is not intended to exclude any qualified designers and installers from the business, nor to hinder the introduction of new dust-collection technology. Specification and Acceptance Testing Acceptance testing, in its simplest form, means "try before you buy." It is the elevator operator's means of insuring that he is getting exactly the dust-collection system he specified and that it is meeting his needs as expected. The operator should thoroughly check the condition and operation of both new and modified dust-collection equipment. He should not pay for a job until he is satisfied with it. This condition should always be specified in design, installation, and purchase contracts. Besides the obvious benefit to the buyer, acceptance testingâas well as warranties and contractually stated break-in periodsâoffers benefits to the seller. By clearly defining these matters in the contract, the seller effectively limits his liability for the job. From another perspective, acceptance testing of dust-collection equipment is an important means of minimizing the hazard of fire and explosion. The competent elevator operator makes sure that his equipment is performing according to design and that it will continue to perform within acceptable tolerances. Besides minimizing hazard, insistence on quality minimizes costs in the long run.
76 The operator who is buying a dust-collection system should specify clearly, to designers and installers, the performance he requires. The specifications should be written into the contract and should include procedures for acceptance testing. The following guidelines are recommended. Guidelines for Specification and Acceptance Testing 1. Specifications The buyer's specifications to the designer should always call for a given level of performance under specific conditions. The designer is responsible for specifying the equipment and installation to meet the owner's performance requirements. A. Legs No visible dust emission and sufficient volume flow and proper design aerodynamics to provide airsweep. B. Enclosed Equipment (conveyors, cleaners, etc.) No visible dust emission from enclosed equipment operating at design capacity, except where structural or mechanical conditions make such performance impossible. Exceptions should be identified in the specifications. C. Scales No visible dust emission from scales operating at design capacity (same exceptions as in IB). No effect on the accuracy of the scales as a result of differential pressure in the system. D. Dust Hoods and Loaders No visible dust emission, at design airflow, from hoods and truck, rail, and vessel loading and unloading. E. Grain Loading and UnloadingâTruck, Rail, Vessel Should comply with local regulations related to the environment and occupational safety and health. F. Driers Should comply with local regulations related to the environment and occupational safety and health. G. Fabric Filter Pressure drop across fabric filter, after 45 days of operation, shall not exceed the maximums stipulated in the agreement and shall not in any case exceed 5 inches of water. H. Blast Gates and Cleanout Opening Location and type. I. Instrumentation Number and location of magnehelic or photohelic gauges, pi tot tubes, and manometers. J. Conveyor-Belt Head Pulley Specify how dust carried over the head pulley will be recovered and conveyed to the dust or grain stream.
77 2. Review of Design to Increase Safety Factor in Performance By reviewing the design, the buyer may be able to specify upgrading of equipment so as to increase the safety factor in performance at little increase in the total cost of the dust-collection system. The buyer and designer can assess the possibilities by checking the following points; A. Types, sizes, and horsepower of fans. B. Filter media. C. Air-to-cloth ratios. 3. The agreement should stipulate adherence to the specified design standards, especially those for inlet and transport velocities, hoods, volume flows, transition fittings, and air-to-cloth ratios. 4. Important Miscellaneous Specifications A. Types and gauges of metal. B. Types and sizes of fans. C. Design static pressure. D. Volume of air to be removed per minute at all takeoff points. E. Nominal transport velocities. F. Air-to-cloth ratios of all fabric filters. G. Types and sizes of motors. H. Explosion-vent ratios on fabric filters. I. Locations of filters. J. Types and sizes of rotary valves on filters. K. Types and locations of monitoring instruments (magnehelic gauges, etc.) for filters. L. Requirement and equipment for compressed air (if applicable). M. Provision for maintenance platforms. N. Initial instructions for operation and maintenance. 0. Certification of bidder's accreditation by permanent committee on qualifications proposed earlier in this section.
78 5. Acceptance Testing The buyer shall perform an acceptance test of the dust-collection system according, to the foregoing specifications. This test should be performed after 45 days of operation. A sample check list for the acceptance test is shown in Table 7-1. TABLE 7-1 Sample Check List for Acceptance Test Description of Item to be Checked Design Value Actual Value at 45 Days 1. System airflow (cfm) 2. Air-to-cloth ratio 3. Fan performance (rpm, cfm, static pressure, brake horsepower) 4. Static-pressure drop across filter 5. Air velocity in duct at Point 1 2 3 4 5 etc.