Qualification test program for emergency chlorine scrubber systems M.R. Gonzalez," R.C. Jain* "Department of Fire Technology, Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas, USA *R.J. Environmental, San Diego, California, USA ABSTRACT Industries worldwide are being charged with assessing the safety and environmental hazards of their operations as a result of increasingly stringent regulations. The widespread use of chlorine in industrial processes including water purification, sanitation of industrial waste and sewage, and manufacture of chlorinated hydrocarbons present concernsrelativeto human health effects and environmental contamination from accidental chlorinereleases.regulations have been developed which require the use of emergency treatment systems in response to these releases and identify minimum chlorine acceptance levels at the point of discharge into the atmosphere. The United States Uniform Fire Code describes regulations for the safeguarding of life and property from the hazards of fire and explosion arising from the storage, handling, and use of hazardous substances, materials, and devices. The primary requirements include operating hazardous material storage rooms in a negative pressure in relation to the surrounding area, and directing the exhaust ventilation from accidental releases to an exhaust treatment system. The exhaust treatment system is required to reduce the maximum allowable discharge concentration of chlorine gas to one-half IDLH (Immediate Danger to Life and Health) which is equivalent to 15 parts per million (ppm) at the point of discharge into the atmosphere. This paper describes a successful qualification test program for emergency chlorine scrubber systems conducted under controlled chlorine release conditions with on-line data collection. Performance evaluations of the scrubbers were based on worst case scenarios and included chlorine release rates of up to 100 pounds per minute as defined in the Southwest Research Institute test protocol. The test results provided vital information on the behavior of chlorine spills, release rates, temperature profiles, flow characteristics, scrubber efficiency, and exhaust stack chlorine emissions recorded from the new scrubber system design.
748 Air Pollution INTRODUCTION Since its commercial production began in 1890, chlorine has been used by the textile, electric power, and chemical industries for a variety of purposes including bleaching, prevention of biofouling, manufacture of chlorine compounds, and water and waste water treatment as presented by G. C. White [1]. Chlorine usage in the United States increased from 2 million tons of chlorine gas and one million tons of liquid chlorine to 12.3 million tons of gas and 7.3 million tons of liquid during the period between 1950 and 1979. Prior to 1950, chlorine was primarily used by the textile industry for bleaching purposes, however, the chemical industry currently uses over 50 percent of the chlorine produced today for the production of over 35 chlorine compounds. These compounds have over 50 end uses ranging from rocket fuel to the manufacture of food products. The largest single use for chlorine compounds has been for the production of ethylene oxide and glycol which are used to make antifreeze fluids and synthetic fibers. As the use of chlorine by industry increased, the need to have safe storage and handling of chlorine containers becomes a primary concern with regard to personnel safety, public health, and protection of the environment Safety criteria have been established in a fire code for the design of indoor storage rooms for compressed toxic gasses and the use of exhaust treatment equipment to handle accidental chlorine releases. It is through the implementation of these types of codes and employee knowledge of the chlorine characteristics that will enable industry to control the number of accidents and their severity as well as minimize injuries to people and damage to the environment Chlorine gas is recognized as a hazardous and toxic material which is corrosive and can cause injury or death if inhaled in significant quantities. The gas is primarily a respiratory irritant, however, sustained exposure at increased concentrations can cause severe reactions and possibly death through suffocation. Two types of gassings can occur as a result of inhaling chlorine vapors, one involves chlorine gas in the dry state while the other involves fumes from an aqueous solution. The more dangerous gassing occurs from a chlorine solution leak since the moisture makes the fumes somewhat more tolerable thus allowing a more excessive amount to be inhaled. Inhaling large doses of chlorine vapors can lead to death due to pulmonary edema causing drowning. Table 1 provides the degree of hazard associated with the chlorine concentrations in air. Chlorine releases can occur from a variety of sources including start up operations, maintenance, equipment malfunction, or component failure. Minor releases can be attributed to gasket failures, valve packing adjustment whereas major leaks result from container rupture, pipeline breaks, broken connections, and possible combustion due to exposure of the containers to excessive temperatures. Several major accidents involving significant releases of chlorine have occurred due to container rupture and improper handling operations. The most common type of containers used for shipping chlorine are the 150 pounds, one ton, and bulk tanks which can carry as much as 16, 30, or 85 tons. Accidents involving chlorine
Air Pollution 749 TABLE 1. EFFECT OF CHLORINE CONCENTRATIONS Chlorine Concentration in Air 1,000 ppm 100 ppm 40 to 60 ppm 30 ppm 20 ppm 6 to 15 ppm 3 ppm 1 to 3 ppm 1 ppm 0.2 to 0.5 ppm 02 to 0.2 ppm Degree of Hazard May be fatal with a few deep breaths. May be lethal. Exposure for 30 to 60 minutes may cause serious injury. "IDLH" - Immediate Danger to Life and Health; coughing, shortness of breath, chest pain, possible nausea and vomiting. Very offensive; will cause person to exit from area immediately resulting in coughing and other discomfort. Throat irritation. Short term exposure limit Definite odor, irritation of eyes and nose. OSHA ceiliing (8 hour time weighted exposure). Household bleach odor concentration. No noxious long-term effects. Odor threshold. releases have caused serious injury and in some cases death as well as damage to animal and plant life. Damage to equipment can also occur due to the corrosive nature of chlorine shorting out electrical contacts and relays which can ignite fires at the plant facilities. Chlorine accidents Some of the more significant accidents have occurred during the transport of chlorine containers as well as by the consumers. The most severe accidents have occurred due to the derailment of rail tank cars which resulted in significant releases of chlorine into the atmosphere. In 1981, a total of 385 tons of chlorine leaked from seven rail tank cars when the train derailed in Estacion Montana, San Luis, Potosi, Mexico. The tank cars were either ruptured or had their valves and protective housings damaged. As a result of this accident, the Mexican government no longer allows this many chlorine cars in a freight train, In 1978, a freight train carrying several tank cars of hazardous waste along with two cars of chlorine
750 Air Pollution derailed near Youngstown, Florida which resulted in 50 tons of chlorine released into the atmosphere. The leak caused 8 fatalities and 138 injuries from a chlorine cloud that measured 3 miles wide, 4 miles long, and 100 feet high. Consumer accidents have occurred primarily at water and wastewater treatment facilities due to mishandling of the chlorine containers or leaks attributed to faulty gaskets or connections. One of the more recent accidents occurred at a waterfilterplant in Morristown, Tennessee. Approximately 2,400 to 3,000 pounds of gas escaped in a leak from two one ton cylinders which were connected through a manifold. This leak forced the evacuation of 4,000 people due to a chlorine cloud that was 5 miles long, one mile wide, and 30 feet thick. Several plant personnel and emergency response team members suffered respiratory irritation and chemical burns. The chlorine vapors caused corrosion of electrical contacts and relays which resulted in a fire in the plant's transformer room. The power to the plant was shut down which could have caused untreated water to be released. In response to these accidents, the Western Fire Chiefs Association published the Uniform Fire Code (UFC) which mandates that indoor storage rooms for compressed toxic gases be equipped with an exhaust treatment system that can handle the contents of the largest cylinder or tank stored. The storage rooms must be designed to operate at a negative pressure to prevent leaks into the atmosphere and direct the exhaust ventilation to an exhaust system. The exhaust treatment system must be capable of diluting, adsorbing, absorbing, containing, neutralizing, burning, or otherwise processing the entire contents from the largest cylinder or tank. The treatment system must reduce the maximum allowable discharge concentration of the gas to one-half DDLH at the point of discharge to the atmosphere. Sizing of the system must allow for processing of the worst case release of gas. Exhaust ventilation systems The most common types of exhaust ventilation systems used to date for chlorine storage rooms include dispersion, packed tower scrubbers, emergency chlorine scrubber systems, and the once through emergency scrubber systems. The dispersion system operates by continuously exhausting the entire room to the surrounding atmosphere without neutralizing the chlorine vapors. This type of system provides protection for the plant personnel but jeopardizes the public living in the nearby communities. This system is the most outdated and fails to meet the UFC. The packed tower system uses an induced draft fan to move the chlorine vapors through packed towers which are irrigated from the top with a neutralizing agent such as caustic. The disadvantage of this system is that it allows a certain percentage of untreated chlorine vapors to be exhausted into the atmosphere at levels which do not meet thefirecode requirements. The time required to wet the packed towers under certain leak scenarios allows for the untreated vapors to be released. Chlorine vapor concentrations are the highest during the first minute of a catastrophic failure and because of the time required to wet the packing, the scrubber efficiency is the lowest. The tower heights present the need for special housings and create unattractive sights.
Air Pollution 751 The third system actually represents the true emergency scrubber system since it is a total containment recycle system that treats the chlorine vapors and returns them back to the room. The system utilizes an ejector-venturi which allows for a quick response and guarantees caustic to chlorine contact for neutralization. The scrubber efficiency allows some amounts of chlorine back into the room which in turn can cause a pressure build up. During large leaks, this pressure could allow for chlorine to be released into the atmosphere through the dampers designed to prevent over pressurization. The scrubber design can be installed within normal room heights. The fourth system is a once through scrubber that combines the use of the ejector-venturi to evacuate the room and a pack tower to allow for the treated exhaust to be released into the atmosphere within the limits required by the fire code. The exhaust can be released into the atmosphere at a greater rate than the chlorine gas rate thus create a negative pressure in the storage room. The chlorine vapors are directed into a caustic storage tank for neutralization and then directed through a packed tower which can be of significant height. Recently a new scrubber system was developed which is a once-through three stage absorption system, consisting of one horizontal spray scrubbing stage followed by two horizontal cross flow packed bed sections. An induced draft fan pulls vapors through the scrubber, where intimate contact with a recirculating caustic solution results in the complete absorption and removal of chlorine. A high efficiency mist eliminator is located in the gas stream, prior to exhaust, to remove any residual caustic solution. The induced draft fan provides a negative pressure throughout the room, ducting, and scrubber. Equipment qualification program Southwest Research Institute, an independent research and development organization located in San Antonio, Texas was contracted to conduct a qualification test program for this new scrubber design. The full scale tests included simulating chlorine leaks of 150, 550, and 1800 pounds to confirm that the scrubber design would meet the UFC requirements for chlorine levels of less than 15 ppm from the scrubber exhaust stack and maintain a negative pressure throughout treatment of the chlorine vapors. The tests conducted for the qualification of the system represented significant quantities of chlorine leaked at catastrophic leak rates which had not been performed before on an emergency chlorine scrubber system. Emergency chlorine scrubber system The scrubbers tested included a system designed to handle a 150 to 300 pound chlorine leak and another designed to handle a one ton leak. Each one of these systems is a once through three stage absorption system which was sized accordingly to provide the appropriate ventilation rates and supply of caustic solution.
752 Air Pollution The scrubber components included a three stage absorber, caustic storage tank, air exhaust fan, caustic recirculating pump, electric control panel, and associated piping. The absorber is placed at the top of the vessel which also contains the integral caustic storage tank. A pump circulates the 20 percent caustic solution through the scrubber which drains to the storage tank by gravity. The exhaust fan was placed downstream from the absorber to ensure that the absorber also operates under a negative pressure to prevent chlorine leakage. The test setup for the chlorine leaks included the chlorine cylinders mounted on a load cell to monitor weight loss, a flash room to provide for controlled leaks, the scrubbers, instrumentation to monitor the temperatures, pressures, and flow rates, and a data acquisition system that would collect data at five second intervals throughout the tests. A schematic of the test layout is provided in Figure 1 which also provides the location of the pressure transducers and thermocouples. The flash room measured 12 x 13 ft with an 11-ft ceiling and contained an 8 x 8-ft and 1-ft deep metal pan to contain the liquid chlorine spill. Sealed windows in the flash room provided complete visible access to the liquid leak discharge and the vaporization of the chlorine at all times. The flash room was coated and caulked with appropriate material to prevent both leakage and chlorine absorption into the wall surface. T-l T-2 T-3 T-4 T-5 T-6 T-7 T-8 Intake air to flash room Hash room Flash room Flash room RJ-150 Air inlet RJ-150 Air outlet RJ-150 Sump RJ-2000 Air inlet T-9 T-10 T-ll T-12 P-l Wt Cl, RJ-2000 Air outlet RJ-2000 Sump Ambient (room) Open Flash room pressure Load cell Exhaust stack chlorine Figure 1. RJ Environmental Chlorine Scrubber Test Process Flow Diagram
Air Pollution 753 The test apparatus and equipment were instrumented to record the following data: a. Flash Room Static Pressure: The static pressure was monitored with a pressure transducer with an accuracy of + 1 inch w.c. b. Chlorine Concentration: The chlorine concentration at the outlet of the scrubber was monitored with an Enterra Model 4000 chlorine analyzer calibrated and certified by the manufacturer. The analyzer was field checked frequently against a calibration kit provided by Enterra. c. Chlorine Release Rate: The chlorine release rate was calculated from the measured chlorine cylinder weight loss versus time. The weight of the chlorine cylinder was monitored continuously with the use of a calibrated load cell. d. Temperature: Temperatures of the ambient air, flash room, scrubber inlet, scrubber outlet, and scrubber sump were measured with type "K" thermocouples. e. Scrubber Pressure Drop: The scrubber pressure drop was determined with a magnehelic differential pressure gauge. f. Scrubber Air Flow: Volumetric air flow rates were measured with an orifice plate at the inlet of the scrubber. The orifice plates were calibrated against a standard pitot tube in accordance to Environmental Protection Agency Method 2. TEST PROGRAM A total of seven tests were conducted on the scrubber systems to provide functional checks as well as confirm the performance specifications. The tests were scheduled to provide for a gradual increase in severity level based on the amount of chlorine released into the flash room. Due to the nature of chlorine, precautions were taken which included informing the test personnel of the safety procedures invoked, providing safety equipment such as breathing apparatus, minimizing the number of personnel in the area of the chlorine cylinders, and closely monitoring the instruments to ensure that the allowable chlorine levels were not being exceeded. Test No. 1, 2. and 3 The first test was a functional check out of the test apparatus, instrumentation, and data acquisition system by utilizing available room air and nitrogen. Once the functional check was completed, a second test was performed using a 150 pound chlorine cylinder and leaking 19 pounds of chlorine in one hour and 22 minutes to ensure that the scrubbers were properly operating and were in fact performing the scrubber operation. The chlorine level measured from the scrubber exhaust stack during this test was 0.1 ppm. The third test included a release of 75 pounds of chlorine into the flash room over a period of one hour and 27 minutes. The
754 Air Pollution chlorine level measured from the exhaust stack during this test was a maximum of 0.2 ppm. These three tests were mandatory before any full scale tests would be allowed. Test No. 4 This test was conducted with the one ton scrubber and had a one ton chlorine cylinder plumbed to the test apparatus. The chlorine leaked into the flash room reached a maximum leak rate of 52 pounds per minute. The test ran for a period of two hours and 21 minutes and leaked a total of 1767 pounds of liquid chlorine. Table 2 shows a summary of the test results and the chlorine release rates as a function of time. The temperature profiles for the flash room, scrubber inlet, scrubber outlet, and the scrubber sump are shown in Figure 2. TABLE 2. 1 TON RELEASE Time, min Release Rate Ib/min Exhaust Chlorine ppm Flash Room Temp. Scrubber Inlet Temp. Scrubber Outlet Temp. Scrubber Sump Temp. 1 52 48 47 84 81 2 42 41 44 84 82 3 40 37 45 85 82 4 39 30 47 85 82 5 37 27 45 85 82 10 37 22 46 88 86 15 35 22 45 92 90 20 35 21 47 97 95 25 33 28 55 107 105 30 34 27 49 104 102 45 29 72 55 111 110 60* - 72 63 114 113 120-69 61 109 108 180-71 65 106 105 240-67 62 106 104 300 -- 71 70 105 103 360-74 74 101 98 "Chlorine Release stopped at 51 minutes after start
Air Pollution 755 120 f Release from 1 ton cylinder 110 - Release Rate = 52 Ib/min Ambient Temp-71 F 100 Scrubber Outlet 90 80 70 60 50 40 30 20 10 0 10 15 20 25 30 35 40 TIME (min) 45 Figure 2. Temperature Profiles As indicated by the temperature readings recorded, the temperature of the flash room dropped instantly, once the chlorine was released into the room and reached a temperature below freezing in about four minutes. Once the chlorine cylinder was emptied, the temperature in the flash room returned to ambient As expected, the temperature of the scrubber sump gradually increased due to the heat of thereaction.figure 3 shows the static pressure of the flash room over time. o er -0.1-0.2-0.3-0.4-0.5-0.6-0.7-0.8-0.9-1.0-1.1 Release from 1 ton cylinder Release Rate - 52 Ib/min Room Volume - 1,600 ft 5 10 15 20 25 30 35 40 45 50 55 60 TIME (min) Figure 3. Flash Room Static Pressure
756 Air Pollution The flash room was maintained under negative pressure throughout the test thus meeting thefirecode requirements. The chlorine levels measured from the exhaust stack was zero thus indicating that the scrubber had removed 100 percent of the chlorine from the vapors. Test No. 5 This test was setup to simulate a catastrophic leak rate of 100 pounds per minute and treating the vapors with the one ton scrubber. In order to obtain the desired leak rate, 550 pounds of liquid chlorine was transferred into a 250 gallon pressure vessel and pressurized with a nitrogen blanket. As a precaution, the 150 pound scrubber was also installed in the test apparatus as a back up system should the one ton scrubber need assistance during the scrubbing operation. The fifth test ran for a period of one hour and 44 minutes with a total of 550 pounds leaked into theflashroom. Due to a maximum leak rate of 100 pounds per minute shown in Figure 4, the temperature in the flash room dropped to below freezing much sooner than Test No. 4. The flash room maintained a negative pressure throughout the test as shown in Figure 5. The temperatures in the flash room during the release are shown in Figure 6. The chlorine levels measured from the scrubber exhaust stack ranged from 0.1 to 0.6 ppm, which was well below the allowable limits set by the fire code. 120 100 80 60 550 Ib release One Ton Release 20 150 Ib release 10 20 30 40 TIME, min 50 60 70 Figure 4. Chlorine Release Rates
Air Pollution 757 Release from 550 pound cylinder Release Rate - 99 Ib/miru Roora Volume-1.600 ft 10 15 20 TIME (min) Figure 5. Flash Room Static Pressure Release from 550 pound cylinder Release Rate = 99 Ib/min Ambient Temp. = 67 F 10 15 20 TIME (min) Figure 6. Temperature Profiles Test No. 6 For this test, the 150 pound scrubber was used to treat a release from a 150 pound cylinder. The maximum release rate obtained during this test was 28.5 pounds per minute as shown in Table 3. The scrubber air flow rate was 280 cubic feet per minute. The entire contents of the cylinder were leaked into the flash room and the maximum chlorine levels measured from the scrubber exhaust was 1.3 ppm.
758 Air Pollution TABLE 3. 150 LB CHLORINE RELEASE Tlme/min 1 2 3 4 5 6 7 8* Tank empty Release Rate Ib/min 28.5 25.8 25.8 23.2 23.2 19.6 6.2 03 Exhaust Chlorine ppm 0.4 0.7 Test No. 7 This test was conducted as a demonstration test to industry representatives and consisted of a leak: from a 150 cylinder using the one ton scrubber as the treatment system. The results of this test were witnessed by engineers from the various companies as part of the education process for understanding the behavior of chlorine leaks. The chlorine levels measured from the exhaust stack were well within the limits set by the fire code. CONCLUSION In meeting the requirements of the Uniform Fire Code for storage of compressed toxic materials, the performance testing of the emergency chlorine scrubber systems provided not only confirmation that the performance specifications were met but also gave industry additional information on the behavior of chlorine spills. For example, the amount of flashing that occurs from the liquid chlorine is estimated at 20 percent, however, during the initial stages of the leak, ICO percent flashing can occur. This places a significant load on the scrubber system and requires appropriate sizing of the system. Another example involves the anticipated temperature rise in the caustic solution during catastrophic leak rates. Temperatures were generally discussed asrisingtoo high and thus causing scrubber damage. The testing program revealed that the temperature rises were well within the operating parameters of the scrubbers. In performing these tests, industries which use chlorine in their processes have exhaust treatment equipment available which represents improved efficiency and has been thoroughly tested. Continued improvements to safety and pollution prevention equipment will help industry address the safety and environmental concerns facing their business operations.
REFERENCE Air Pollution 759 1. White, G.C. 'Handbook of Chlorination and Alternate Disinfectants/ Chapter 1, Chlorine: History, Manufacture, Properties, Hazards, and Uses. pp. 1-88, Van Nostrand Reinhold, New York, 1992.