Risk Assessment for Hexamine Nitration into RDX

Galante, Erick Braga Ferrão; Costa, Daniele Mesquita Bordalo da; Haddad, Assed Naked; Santos, Isaac José Antônio Luquetti dos

doi:10.5028/jatm.v6i4.380

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ORIGINAL PAPERS • J. Aerosp. Technol. Manag. 6 (4) • Oct-Dec 2014 • https://doi.org/10.5028/jatm.v6i4.380 copy

Risk Assessment for Hexamine Nitration into RDX

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT:

Explosives are widely used in extraction of ores, melts and fuels and in the safe and economical demolition of structures. These applications demonstrate the value of explosives to society and the reason why they are manufactured worldwide despite the hazard of their preparation. Hence, this paper focuses on the manufactory of the military explosive Hexogen (also known as RDX). The characteristics of the process are described by the analysis of a specify manufactory plant. The chosen analysis tool is the Hazard and Operability Study - HazOp. Historically, this methodology has been applied at chemical industries and is used in industrial process operability analysis. This study analyses seven critical nodes in the RDX manufacturing process, identifies several deviations, and causes and consequences. From these results, improvements in the units are suggested and actual conditions discussed. It is important to remark that this work is an initial approach to analysis of the manufacturing process of RDX using the HazOp methodology.

KEYWORDS:
Risk Assessment; Explosives; Nitration; Hexogen; RDX; HazOp

Quantity	Type of equipment
1	Hexamine feeder
1	Pump for HNO₃ @ 60%
1	Vacuum pump
1	Vessel for feed water
3	Hexamine rated feeder
1	Exhauster
2	Boiler
2	Vacuum filter
3	Nitration vessel
2	Emergency neutralization vessel
1	Waste water vessel
1	Support tank for the vacuum pump
1	Vessel for HNO₃ @ 10%
2	Vessel for HNO₃ @ 60%
1	Vessel for HNO₃ @ 99%
1	Separation vessel
2	Heat exchanger

	Meaning	Example
None	None of the objectives is achieved	No flow
More, Bigger	Quantitative increase in a parameter	More temperature
Less, Minor	Quantitative decrease in a parameter	Less pressure
Part of	Just part of the objectives is achieved	Part of the yield
Reverse	Occurs the opposite of what one expects	Reverse flow
Other	Full replacement	Liquids in a gas pipe

Parameter	Guide word	Deviation
Flow	None, Less, More, Reverse, Other, Also	None, Less, More, Reverse, Other, Contamination
Pressure	More, Less	More pressure,Less pressure
Temperature	More, Less	Higher temperature, Lower temperature
Viscosity	More, Less	More viscosity,Less viscosity
Reaction	None, Less, More	No reaction,Reaction incomplete,Intense reaction

Node	Parameter
1	Flow, Pressure, Temperature
2	Flow, Temperature, Reaction rate
3	Flow, Temperature, Reaction rate
4	Flow, Pressure, Temperature
5	Flow, Pressure, Temperature
6	Flow, Temperature
7	Flow, Temperature

Guide word	Deviation	Cause	Detection	Consequences	Mitigation
Flow	None	Vacuum filter malfunctioning Defect in the tank for emergency transfer	Indication in the flow meter Visual inspection Under functioning pump to HNO₃@60%	Breaking the vacuum pump Reduced yield factor for nitration	Flow reversal of the tank to the vacuum pump and boiler 2 through valves Flow increase for the tank to HNO₃, 60% through valves
	Less			Failure separation tank Flow Increase for the baffle for wastewater Flow decrease to the tank to vacuum pump Flow decreased to absorption of HNO₃
	More		Leakage or malfunction of the pump to HNO₃ Over functioning pump to HNO₃@60%	Breaking the vacuum pump Increased temperature and fire hazard Increased pressure within the vessel Flow increase for the baffle for wastewater Flow increase for the tank to vacuum pump	Stopping the flow
Pressure	Less	Flow Decreased	Lowering the temperature	Reduced yield factor for nitration Flow decreased to baffle for wastewater	Decrease Flow to tank for HNO₃@60% Installation of measuring instrument Pressure
Pressure	More	Flow Increase	Increasing the temperature	Flow increase for the baffle for wastewater Breaking the vacuum pump	Increasing the flow to the tank HNO3@60% Installation of measuring instrument Pressure
Temperature	Less (< 12ºC)	Failed vacuum filter Temperature change in pump HNO₃@60%	Checking through instruments (thermometer) Inspection through the inspection location	Precipitation of the product Vacuum pump failure	Decrease flow to tank for HNO₃@60% Perform preventive maintenance control systems and operation of feed valves of the heating fluid and cooling
Temperature	More (> 15ºC)	Failed vacuum filter Temperature change in pump HNO₃@60%		Over-Pressure vessels Increased speed reaction Risk of explosion due to a sudden pressure relief in a closed vessel Leak of NOx Interruption of production Loss of quality Yield loss Risk of fire from overheating	Increasing the flow to the tank HNO₃ @60% Perform preventive maintenance on control systems and operation of temperature control valves

Guide word	Deviation	Cause	Detection	Consequences	Mitigation
Flow	Less	Hexamine feeder failure Failure dosage HNO₃@99%	Decreased production of the nitration vessel 3 Overheating innitration vessel 3	Interruption ofproduction downstream	Manual duct repairReplacinghexamine feeder
Flow	More	Hexamine feeder failure Failure dosage HNO₃@99%	Increased production of the nitration vessel 3 Overheating innitration vessel 3 Flow in emergency dump tank	Overload nitration vessel 3 Pressure and consequent increased risk of explosionInterruption of operation of the discharge valve background	Replacing hexamine feeder Emptying the nitration vessel through bottom discharge valves
Temperature	Less (< 12ºC)	Hexamine feeder failure Failure dosage HNO₃@99% Failure in the heat exchanger	Reduction of refrigerant flow return with brine Checking through existing instruments (thermometer)	Increased returnchilled water brine Decreased feed flow of refrigerant brine Damage to the product Interruption of Reaction	Flow Decrease feed coolant brine
Temperature	More (> 15ºC)		Increasing the flow of refrigerant return with brine Checking through instruments (thermometer)	Over-Pressure vessels Increased reaction speed Risk of explosion due to a sudden pressure reliefin a closed vessel Leak of NOx in the workshop Interruption of production Loss of quality Yield loss Risk of fire from overheating	Increasing flow of refrigerant feed brine
Reaction	None	Failure feeder hexamine Failure dosage HNO₃@99%	Checking through instruments (thermometer)	Decreased production of nitrous gases Overheating the first and second nitration vessels	Flow decreased to the tank to discharge emergency
	Less		Checking through instruments (thermometer)		Flow decreased to the tank to discharge emergency
	More		Increased Pressure in the first nitration vessel Checking through existing instruments (thermometer)	Increased rate of release of nitrous gases Overheating in nitration vessels 1 and 2	Flow increased to the tank to discharge emergency

Guide word	Deviation	Cause	Detection	Consequences	Mitigation
Flow	None	Failure feeder RDX Failure tank HNO₃@99% Clogging the duct Driving	Overheating in boiler Visual InspectionReduced flow baffle for boiled water	Damage to the boiler Product loss Risk of fire	Replacing the feeder for hexamine Maintenance dosing for hexamine Duct repair manual
	Less			Damage to the boiler Product loss Risk of fire
	More	Failure feeder RDX Failure tank HNO₃@99%	Overheating in boiler Visual Inspectionflow Increase for boiled water baffle	Damage to the boiler Product loss	Replacing the feeder for hexamine Maintenance dosing for hexamine Interruption of proceedings
Temperature	Less (< 12ºC)	Decreased flow between equipment	Verification by local inspection Checking through instruments (thermometer)	Loss of income from reaction Interruption of proceedings	Use of temperature control valves
Temperature	More (> 15ºC)	Increased flow between equipment		Over-pressure vessels Increased speed reaction Risk of explosion due to a sudden pressure relief in a closed vessel Leak of NOx	Use of drain valves forregularization Use of temperature control valves
Reaction	Less	Failure feeder RDX Duct obstruction driving	Cooling inboilers 1 and 2	Interruption of productionLoss of quality Yield loss System under heating	Interrupting the process to repair feeder in
Reaction	More	Failure feeder RDX	Heating inboilers 1 and 2	Interruption of production Loss of quality Yield lossRisk of fire from overheating Leak of NOx in the workshop	Interrupting the process to repair feeder RDX

Guide word	Deviation	Cause	Detection	Consequences	Mitigation
Flow	None	Failure at first boilerFailure tank HNO₃@99% Duct obstruction in driving	Interruption of the production processUnder heating the boiler 2 Reduction of flow baffle for wastewater	Interruption of production	Maintenancefirst boiler Maintaining the tank HNO₃@99% Duct repair manual
	Less			Loss of production quality due to the contribution of the advancement of chilled water
	More	Failure boiler 1 Failure tank HNO₃@99%	Interruption of the production process Overheating the boiler 2 Flow presence of the boiler 1 to the emergency dump tank Flow Increase for the baffle wastewater	Insufficient progress chilled water to maintain operations Interruption of operation of the discharge valve background	Maintenance first boiler Maintaining the tank HNO₃@99%
Pressure	Less	Decreased flow at first boiler	Interruption of the production process Verification by instruments Breaking duct driving	Decreased Flow for the heat exchanger Increased feed of cold water	Maintenance first boiler Installing a meter or pressure gate Installation and calibration of Pressure relief valves are configured as recommended in regulations
Pressure	More	Increased flow at first boiler	Checking through the instruments consolidated control panel unit	Risk of explosion due to a sudden pressure reliefin a closed vessel
Temperature	Less(< 12ºC)	Decreased Pressure on boiler 1 Flow Increase for the baffle for wastewater	Verification by local inspection Checking through instruments (thermometer) Verification flowto the baffles	Decrease in advanceof cold water Increase in reaction time Reduced yield factor	Installation of controlvalves temperature Installation flush valves bottom
Temperature	More(> 15ºC)	Increased Pressure in the kettle 1 Flow decreased to baffle for wastewater		Risk of explosion due to a sudden pressure relief in a closed vessel Risk of Explosive initiation

Guide word	Deviation	Cause	Detection	Consequences	Mitigation
Flow	None	Failure in the tank for HNO₃@60% Failure in the first boiler Duct obstruction in driving	Under heating of the heat exchanger	Pressure decrease the heat exchanger Heating in the heat exchanger	Increasing the flow of feedstock feeder RDX
	Less		Under heating of the heat exchanger		Increasing the flow of feedstock feeder RDX
	More	Failure in the tank for HNO₃@60%Failure in the first boiler	Overheating of the heat exchanger	Increased Pressurein the heat exchanger Cooling Heat Exchanger	Reducing the flow of raw material in the feeder RDX
Pressure	None	Gas Leak	Visual inspection Checking through instruments (Pressure gauge) or control panel operating parameters Decrease the temperature in the heat exchanger	Interruption of production	Installing a meter at this point Pressure Installing a valve for controlling the output of nitrous gases at this point
	Less	Increased of NOx output		Ineffectiveness of heat exchange, compromising the yield and economic balance of reaction
	More	Decreased output of nitrous gases	Visual inspectionChecking through instruments (Pressure gauge) or control panel operating parameters Increased temperature in the heat exchanger	Risk of explosion due to a sudden pressure relief in a closed vessel Risk of explosive initiation
Temperature	Less(< 60ºC)	Decreased pressure Reduction of flow entry of cold water in the heat exchanger	Verification by local inspection Checking through instruments (thermometers) Reduction of flow chilled water return flow increase in feed cold water	Ineffectiveness of heat exchange, compromising the yield and economic balance of reaction	Use valve for controlling the water outlet from the cold heat exchanger
Temperature	More (> 80ºC)	Increased pressure Flow of increased cold water inlet in the heat exchanger	Verification by local inspection Checking through instruments (thermometers) Increasing the flow of chilled water return Decreased feed flow cold water	There is no risk of explosion, just leak fluid heated, which creates potential for burns

Guide word	Deviation	Cause	Detection	Consequences	Mitigation
Flow	None	Mechanical failure in the heat exchanger Failure in the tank for HNO₃@60% Duct obstruction driving	Decreasing the amount of produced hexogen	Under load in the vacuum filter	Regular benchmarking of verification of equipment (meter) Installing a control valve flow Duct repair
	Less		Decreasing the amount of produced hexogen	Under load in the vacuum filter
	More	Mechanical failure in the heat exchanger Failure in the tank for HNO₃@60%	Increasing the amount of produced hexogen Identification of overflow material	Overhead in the vacuum filter	Regularization of flow through safety valves Performing batch filtering
Temperature	Less	Flow decrease in cold water	Verification by local inspection Checking through instruments (thermometer)	Interruption of operation of the filter	Establish procedures and regular targets for maintenance of existing control systems
Temperature	More	Flow increase in cold water		Interruption of operation of the filter Damage to the filter	Installing a hardware check (thermometer) Interrupting the natural cooling process for product

Guide word	Deviation	Cause	Detection	Consequences	Mitigation
Flow	None	Failure in vacuum filters Clogging the duct Driving	Visual Inspection Verification of the final product - not or poorly crystallized Flow Increase for the tank HNO₃@60%	Low yield factor Under functioning the hood	Repair of vacuum filters Maintenance or replacement duct Driving
	Less	Failure in vacuum filters Clogging the duct Driving		Low yield factor Under functioning the hood
	More	Failure in vacuum filters		Low yield factor Over functioning the hood	Maintenance or replacement duct Driving

Node	Node description	Key equipment	Recommendations
1	Array of vessels for waste and clean water for dilute HNO₃	Water vessels	Installation of control valves to assure flow management. Implementation of level and temperature instruments. All instrumentation should be integrated.
2	Connection between nitration vessels	Nitration vessel	Implementation of a system to dose hexamine automatically Installation of a venting system in the equipment to prevent overpressure and the consequent risk of explosion is recommended. Use of an empty dump tank and a draining valve at bottom. Favor mechanical valves over electronic ones in this key position.
3	Connection between the nitration vessel and the boiler	Post-nitration boiler	This operation (boiling) will release the nitrogen oxide gases, requesting a venting/exhaustion system. It is necessary a mechanism to interrupt the operationin case of overflow. Deviations in temperature are directly related to flow.
4	Connection between boilers	Boiler	Deviations for flow can be identified by the presence of material in the emergency dump vessel. In this situation the risks involved and response mechanism are analogous to those in node #2. Installation of a pressure gauge for the control parameter. Temperature effects should be controlled with the implementation of instruments and a command and control system.
5	Connection between boiler and heat exchanger	Heat exchanger	Dosing accurately the hexamine is key to avoid deviations in flow and temperature. This operation (boiling) will release the nitrogen oxide gases, requesting a venting/exhaustion system.
6	Connection between the heat exchanger and the vacuum filter	Vacuum filter	Installation of control valves and periodic maintenance, as well as a flow meter should be considered Installing equipment for monitoring as well as for cooling or heating the product to be filtered should be considered
7	Connection between the vacuum filter and the RDX recovery pan	Filtering system	Deviations for this node (node #7) are observable through loss of product quality and operational variation of the exhaust system. A possible mitigation is to ensure maintenance of this equipment.

Departamento de Ciência e Tecnologia Aeroespacial Instituto de Aeronáutica e Espaço. Praça Marechal do Ar Eduardo Gomes, 50. Vila das Acácias, CEP: 12 228-901, tel (55) 12 99162 5609 - São José dos Campos - SP - Brazil
E-mail: submission.jatm@gmail.com

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[1] Author for correspondence: Erick Braga Ferrão Galante | Instituto Militar de Engenharia - Departamento de Engenharia Química | SE/5 - Praça Marechal Tibúrcio 80, Rio de Janeiro/RJ | CEP: 22290-270 - Brazil | Email: egalante@ime.eb.br