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FEMA/IFRA NA SAFE PRACTICES FOR SPRAY DRYER OPERATIONS Maintaining safe and healthy workplaces is a matter of utmost importance to FEMA, IFRA NA, and their members. This document is intended to assist members of the Flavor and Extract Manufacturers Association and the International Fragrance Association North America with maintaining safe practices in spray dryer operations. Because of the unique nature of each workplace, the information in this report should be considered only as a general guide; it is advisory in nature and informational in content. Neither FEMA nor IFRA NA are responsible for either the use or nonuse of this information, or any actions, or failure to act, in any specific workplace based on reliance on this document. It is not a formal policy, standard or regulation, and this document does not create any new legal obligations nor does it relieve members of existing regulatory requirements. It is your individual responsibility to verify this information as it applies to your workplace.
INTRODUCTION Explosions in spray drying operations have caused serious industrial accidents resulting in severe damages, injuries, and deaths. The aim of this document is to help determine critical safety parameters in spray drying operations. This should not be considered as a risk assessment. For all equipment and processes a team of qualified people should carry out a formal risk analysis. According to OSHA’s Hazard Communication Guidance for Combustible Dusts, 5 conditions are necessary to have an explosioni: 1. 2. 3. 4. 5.
Combustible dust Ignition source Oxygen Dispersion of dust particles in sufficient quantity and concentration Confinement of the dust cloud
To avoid explosion, prevention consists of exclusion of at least one of these above conditions. To mitigate/suppress explosion effects, protective measures include: explosion relief vents, explosion suppression systems, operation with inert atmosphere, explosion containment and building design, and prevention of secondary explosions. Critical steps in spray drying operations: 1. OPERATING PROCEDURES
Standard Operating Procedures (SOP) based on risk evaluations should be written for all steps: - Emulsion preparation - Start-up - Normal operation - Shut-down - Cleaning - Maintenance - Emergency shut-down - Restart after an emergency shut-down At a minimum, initial and refresher training should be supplied to operators.
2. EMULSION PREPARATION AND FEED LINE Phase separation could allow feeding of pure organic liquid phase into the dryer, producing extremely flammable vapors that may be beyond the capacity of the explosion protection system The emulsion preparation (formula) and process should be evaluated to ensure that the resulting dried powder does not exceed the safety rating of the drying equipment Flammable liquids and combustible powders will be handled in the mixing area, NFPA standardsii (Hazardous area classification or zoning) - for example explosionproof equipment, and adequate ventilation should be applied Proper selection of emulsifying agents, primary emulsifying systems, and subsequent feed tank agitation designed to prevent phase separation should be considered Appropriate checks of emulsion agitation should be assured to avoid phase separation along the entire run Operators should be trained and alert to detect separation and to shut-down operations if detected. If separation is found to occur, equipment or process control changes should be implemented. 3. SAFETY PROTECTION CONCEPT Design of protection should be based upon the ability of dust to explode which is classified as follows: Dust Explosion Class Characteristics St 0 St 1 St 2 St 3 Hybrid Mixture (solvent + powder):
Kst (Bar m s-1) 0 >0 <200 >200 <300 >300 Kmax >400
No Explosion Weak Explosion Strong Explosion Very Strong Explosion Very Strong Explosion
Kst = explosion severity constant for the powder, related to maximum rate of pressure rise.
A Hybrid Mixture is hazardous for the following reasons: 1. When combustible dusts and flammable vapor mixtures are present below their respective flammable limits, they may form an explosive (hybrid) atmosphere when mixed together. 2. Dust mixtures in the presence of flammable vapors may be more easily ignitable. 3. Course powders that normally would not cause an explosion may cause an explosion when they are in the presence of a flammable vapor or gas.
Open cycle spray dryers for encapsulating organic liquids should be designed for an explosion protection rating corresponding to the adequate dust explosion class. Explosion vents should be directed to a safe outside area. Direct fired units should be provided with an interlock to prevent flammable material from travelling to the burner in an upset condition (e.g.) air failure. Ductwork or equipment interconnected with the dryer should be provided with isolation or protected against ignition or explosion spread. As electrostatic ignition of flammable vapors or dusts is a great potential hazard, conductive materials should be used as far as possible. Spark discharges can be avoided by grounding all conductive objects [plant units, ancillary equipment, drums, big bags (i.e.) super sacks, products, etc…]. People should also be grounded through the use of anti-static clothing / shoes and conductive floors. Inlet air and outlet temperatures should be controlled and limited to the maximum established together with the spray dryer equipment supplier. Only spark free fans should be installed. The pressure rating for the dryer system should be reviewed against the design of the dryer building to ensure that adequate pressure relief is provided for both. The use of Explosion Suppression Systems, flameless venting and nitrogen inerting should be evaluated.
4. CLEANING AND MAINTENANCE Deposits of thick layers of wet product on the dryer walls should be avoided by all practical means including mechanical, limited feed rate, along with periodic inspection and testing. New products present a particular hazard in this area, until process parameters can be confirmed. Maintenance and cleaning schedules for inlet filters on both indirect and direct fired dryers should be established and maintained. Suppression systems, safety switches and interlocks should be tested periodically to ensure proper performance. Devices inside the dryer that could cause friction (atomizer) should be inspected during use and have regularly scheduled maintenance. Mechanical integrity of the equipment should be tested periodically (for example, the presence of cracks or corrosion will degrade the reduced pressure rating). 5. ENVIRONMENT
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To avoid odor and VOC contamination, a treatment of outlet air may be installed. When an incinerator is used, flash-back should be avoided by appropriate devices.
OSHA 3371-08, “Hazard Communication Guidance for Combustible Dusts,” U.S. Department of Labor, Occupational Safety and Health Administration, 2009. ii NFPA 33, “Standard for Spray Application Using Flammable or Combustible Materials,” National Fire Protection Association, 2011. NFPA 61, “Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities Explosions,” National Fire Protection Association, 2008. NFPA 68, “Standard on Explosion Protection Using Deflagration Venting,” National Fire Protection Association, 2007. NFPA 69, “Standard on Explosion Prevention Systems,” National Fire Protection Association, 2009. NFPA 499, “Recommended Practice for the Classification of Combustible Dust from the Manufacturing, Processing, and Handling of Combustible Particulate Solids,” National Fire Protection Association, 2008. NFPA 654, “Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids,” National Fire Protection Association, 2007.
