Heat Exchanger Design and Safety Analysis: DME Production Report

This report presents a detailed analysis of a heat exchanger design for the production of dimethyl ether (DME) from methanol, with a target output of 250,000 gallons per day. The primary objective is to design a heat exchanger to cool a mixture of DME, water, and methanol from 280°C to 98°C. The report emphasizes safety considerations throughout the design process, addressing potential hazards associated with DME, such as inhalation risks and flammability, and outlining safety measures like PPE, ventilation, and vapor detection. It also covers safety protocols related to hot water exposure, including insulation, protective gear, and material selection. Furthermore, the report discusses the integration of control loops within the system, highlighting the need for both active and passive safety controls, including alarms, automated actions, and backup systems to ensure operational safety during various failure conditions. The design parameters, including shell and tube specifications, tube materials, flow rates, and the importance of continuous monitoring and inspection, are also detailed. References to relevant literature are included to support the analysis.

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Safety concerns in the Design:
Safety and health concerns to be considered in the design are presented in the following
discussion part of the write-up. The discussion is spanned to evaluate the Safety with DME,
Safety aspects with the hot water and finally the control loops in the system.
(i) Safety with Dimethyl Ether(DME)
Dimethyl Ether should be restricted from entering into the human respiratory system, If incase
DME is inhaled into the human respiratory system, it can create serious implications to the eye,
throat and nose. Implications can range from minor irritations to the serious infections, Hence
inhaling the same into the respiratory body need to be curtailed with proper equipment. When
the level of exposure of DME is quite high, it can create a range of problems to the individuals
that can include headaches, dizziness, and lightheadedness and also will create even the loss of
consciousness as well. Severity and the time of exposure to the vapors of DME will create the
specific complication in the victim. At times when operators are exposed to the liquid DME, the
skin will get severe frostbite. Other important aspect is the dangerous levels of fire hazard with
the substance it is highly flammable and hence need to be protected with all the measures of fire
protection. Typical means of employing non contact gloves for DME as well using respiratory
shielding will protect the operators working in the region from getting contact with DME. Also
exposure meters in the location will alert the surrounding with the level of DME in the location
and thereby will help the operators to identify the hazard and to take up the necessary protection
measures (King 135). Further the locations should be provided with exhaust ventilations to
enable quick dissipation of the vapors.

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 Typical implications to the current design include,
 Operator safety provisions – PPE during operations
 Providing with alarms for the DME vapors
 Provision of Exhaust ventilation to let the DME vapors to move off the location in case of leaks
 Providing provisions to verify the seals of the valves etc are intact or not.
(ii) Safety with hot water
Hot water exposure will cause implications to the operator or the victim in proportion to the
temperature of the water as well in proportion to the time of exposure. If the hot water is
exposed for long time, it will create burns and serious wounds on the skin of the person
exposed to the hot water. Further sprinkling of hot water on to the face, eyes and other vital
organs can create serious implications of loss of sight etc. There is need for taking
precautions by continuously monitoring the health and well being of the systems by keeping
the precautions and other operational controls intact. Chronicle inspection of the pipe
lines(Abedi 770), adding insulation to the hot exposed parts of the heat exchangers and other
hot water carrying components, condition monitoring of the valves etc is necessary to ensure
safety in dealing with hot water and hot water carrying parts in the systems.
 Implications to design
 Keeping the operators safe from the impact of the hot water
 Enabling insulation (lagging) on the pipes carrying the hot water and steam if any.
 Providing operators with the heat resistant gloves and face shield while operating with
the heat exchanger.

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 Selection of the material of the HE with required thermal resistance and strength along
with corrosion resistance at the given higher temperature conditions.
(iii) Safety with the control loops:
Control loops are often automated and integrated in the operational cycles of the process.
They are more dynamic and virtually will not offer any sort of protection to the systems
when they get into the unpredicted conditions. Hence these active systems will be integrated
with passive safety controls in general. Typical conditions like high pressure protection in the
pipeline will be ensured by the passive controls in the system. Protection of the systems by
enabling alarms and auto actions are key features of these safety processes integrated into the
main stream control loops in the system. Apart from these systems, the safety control loops
also will be having characteristics like backing up the control units during power failure,
hazardous conditions etc (Liptak 114). They do enable the control operations to happen in
any type of system failures.
 Implications to design
 For control loops enabling safety process loops integrated.
 Typical controls on highest temperature allowed
 Typical control on the highest pressure allowed.
 Other external controls like fire detection and system halt controls need to be placed.

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References
Abedi, Parisa, and Mohammad Shahriari. "Inherent safety evaluation in process plants—a
comparison of methodologies." Open Chemistry 3.4 2005, p. 770.
King, Ralph. Safety in the process industries. Elsevier, 2016, p.135.
Liptak, Bela G. Instrument Engineers' Handbook, Volume Two: Process Control and
Optimization. CRC press, 2018, p.114.