Keeping Chlorine Accidents Under Control

Controlling Chlorine Incidents: Use of Chlorine Emergency Units for Chlorine and Hydrogen Chloride Production and Processing

Chlorine and hydrogen chloride production have always posed a risk to people and the environment, and therefore require appropriate safety measures. GEA offers chlorine emergency units specifically developed to prevent uncontrolled gas leakage in such applications. These devices are spray gas scrubbers that provide top-level operational safety thanks to their immediate availability and simple design. Industrial production of chlorine and hydrogen chloride and the diverse processes in which they are used in chemical and water treatment industries require special safety measures when handling such highly toxic chemicals. All potential risks resulting from accidents during production, transport and storage must be considered, and gas leaks must be detected immediately and chlorine and hydrogen chloride must be prevented from escaping into the atmosphere. Chlorine leaks have occurred in many cases during the filling of storage tanks and during the stacking of chlorine cylinders, each containing 500 kg or 1000 kg, in storage areas. Chlorine and hydrogen chloride are most safely disposed of by chemical absorption in aqueous caustic soda solution. This process releases a high amount of heat. nH2O + 2NaOH + Cl2 ï (n + 1) H2O + NaCl + NaOCl nH2O + NaOH + HCl ï(n + 1) H2O + NaCl The basic requirements for the relevant technical equipment are as follows: • The system must be ready to operate at full capacity immediately. • It must have high operational safety.

Spray gas scrubbers as emergency units

Spray gas scrubbers meet these requirements perfectly. They serve not only as gas scrubbers but also as fans. Thanks to their simple design with no moving parts in the gas passage, they are extremely reliable and ready to operate at full capacity immediately. Another very useful advantage is their ability to adapt the load according to changing operating conditions. In spray gas scrubbers, the washing liquid is sprayed in droplet form through nozzles. In the spray tube, the droplets transfer their kinetic energy to the gas flow and thus increase the pressure. The pressure created according to the spray principle can be used for drawing in and transferring gases as in mechanical fans. The contact between gas and liquid makes the spray fan a perfect gas scrubber. The washing liquid sprayed by the drive nozzles provides a continuously renewed heat transfer surface for the gas flow. The high relative velocity between gas and liquid droplets creates turbulence in the droplet area and thus good mass transfer coefficients. The high separation ratio comes from its special position among gas scrubbers and results from the simultaneous effects of washing and transfer. Only gas particles at the interface of the droplets are transferred and compressed. The gas in close contact with the washing liquid and purified of pollutants is what passes through. The unpurified gas located away from the droplets does not increase in pressure. This gas returns to the gas scrubber. Spray gas scrubbers are co-current scrubbers. They are used for process needs requiring large quantities of circulation, for example containing high quantities of pollutants or in thermal processes. For this purpose, chlorine absorption is a common classic application. The separation efficiency required for chlorine and hydrogen chloride absorption is generally achieved with two jet spray gas scrubbers connected in series (see Figure 1). Figure 1: Fixed, counter-flow column, chlorine emergency spray gas scrubber. Gas intake rate; approximately 1,000 m³/s, absorption capacity: 150 kg/s chlorine GEA offers this type of emergency chlorine unit in four standard sizes for room evacuation. The quantity of gas to be captured and transferred determines the system size. Figure 2 shows a unit with a chlorine absorption capacity of 1,000 kg. Figure 2: Fixed, 2-stage emergency chlorine spray gas scrubber with downward counter-flow column. Gas intake rate: approximately 5,000 m³/s, absorption capacity: 1,000 kg/s. Figure 3 shows a mobile emergency chlorine unit provided by GEA with an absorption capacity of 150 kg/s. It is particularly used in tank car accidents and can be transported to the accident site by truck, rail or helicopter. Figure 3 shows a mobile emergency chlorine unit provided by GEA with an absorption capacity of 150 kg/s. It is particularly used in tank car accidents and can be transported to the accident site by truck, rail or helicopter.       Figure 4 shows another fixed emergency chlorine unit for a tank car unloading station with an absorption capacity of 50,000 kg chlorine. This system has three spray stages due to special requirements for outlet air purity. Figure 4: Fixed emergency chlorine unit with absorption capacity of 50,000 kg chlorine. Gas intake flow: 10,000 m³/s. Larger systems for chlorine or hydrogen chloride absorption are not only used as emergency units with capacities of 50,000 kg/s chlorine or 20,000 kg/s hydrogen chloride, but are also used in the startup or shutdown of large production facilities and operate partially at low load continuously. Such units easily handle operating conditions with widely varying loads. Figure 5 shows an example of a system designed for 15,000 kg/s hydrogen chloride absorption. During several days of operation, this system transfers 15 kW of heat through a plate heat exchanger to the cooling water. In another application, this unit purifies 35,000 kg/s of tail gas at high operating pressures.    

Summary:

The design examples presented above demonstrate that spray gas scrubbers function excellently for the safe handling of chlorine and hydrogen chloride because of the following fundamental characteristics: • Immediately available and ready to use at full capacity, • High operational reliability, • Regeneration capability, • Extremely flexible (load adaptation), • Simple and compact design, • Resistant to wear and tear, requires minimal maintenance, • User-friendly, • Reasonable manufacturing and operating costs. İlker Damar / Norbert Strieder - Roland Luchte - Sales Manager - Industrial Applications - GEA Group Norbert Strieder / Chemical Applications Center - Marketing & Sales Manager - GEA Group Roland Luchte / Chemical Applications Center - Emissions Control-Gas - Cleaning Systems Director - GEA Group