©  Copyright 2013 Chemical Engineering & Gas Processing Multipurpose micro reactor and catalyst test setup for DME production This system is a multi purpose reactor comprising a refrigeration system, steam generator and six adiabatic fixed   bed micro reactors which are equipped with a pre-heater, temperature and pressure controller. This system has  been designed so that the connection of the input and output reactors with gas chromatography is possible to  measure the concentration of materials at any location of the device. In general, three of these reactors are in  parallel which considered in order to DME synthesis from methanol and three series reactors has been embodied at  the other side of device to produce propylene from DME during the catalytic reaction.  Each reactor has an individual preheater in order to heating and phase change of methanol feed. For each of the  DME synthesis reactors, The HPLC pump has been employed to supply the liquid feed at the suitable  flow rate.  They control the outlet pressure and supply the feed with a high accuracy in lab scale range (0.01 ml per min).   Then, DME as an intermediate is feed into the propylene synthesis reactors. The run status of the pumps is  accessible for operator on the screen of HMI (Human Machine Interface). The outlet of each pump is equipped with  a pressure gauge  and pressure safety valve. Since  maximum temperature input  to the pumps is equal 60 °C, this  equipments have been isolated by a check valve from the next section which operate at high temperature. Also, two  pressure transmitters (PT) have been located at the inlet and outlet of the reactors to monitor the system pressure  and maintain acceptable levels of safety. A pressure and high pressure set point are programmable for these   instruments to active the  high  pressure alarm and ESD (Emergency Shut Down)  in times of crisis. In addition, the  system pressure is regulated by means of the back pressure regulators which are mounted on the vapor stream line  leaving the DME flash tanks. Figure 1 shows a general view of the setup.  Figure 1. The schematic of experimental apparatus The Pre-Heaters directly is connected to the 3/8” ID reactor via the traced Stainless Steel tube. The temperature of   bed catalyst in each reactor has been measured by a submerged thermocouple which is placed in middle of the  catalyst bed. Furthermore, two thermocouples have been located at different  positions in the shell to control and fix  the ambient temperature of the reactor. The thermocouples are connected to the microprocessor based thermo  regulator. Also, as the temperature of each of the pre-heaters can be adjusted on the heater control station the  actual steam temperature is also monitored by thermocouple on the HMI. The outer shell of the reactor is insulated  by glass wool layer to reduce heat losses and divided into two zones: a high temperature zone (Zone I) which  tubular reactor is placed and a low temperature (LT) zone (zone II) which is downstream of the HT zone to maintain  almost zero temperature gradient in the shell. The shell is covered by the heating elements which enables local  heating of the reactor surrounding and provides better temperature control of the reaction zone. The temperatures  of zones are adjustable and visible on the heater control panel. Under this condition, an ideal adiabatic condition is  provided within the catalyst bed. A schematic of adiabatic fixed bed reactor is depicted in the figure 2.    Figure 2. Adiabatic fixed bed reactor schematic For temperature maintenance of the lines and prevention of the possible methanol and water condensation, the  effluent gases were heated by means of the electric heat tracing system. The heating tapes has been mounted on V   the stainless steel tubes and covered with thermal insulation to retain heat losses from the pipe. The temperature is  set by the heat tracing control panel and heat generated maintains the temperature of the pipe. The outlet products  from each of parallel reactor containing  DME,  water and unreacted methanol  are passed through a shell and tube  heat exchanger to cool down to the ambient temperature. Cooled products are sent to a gas–liquid separator and  dimethyl ether as a gas phase is transferred to the propylene synthesis reactors from top of the flash drums. The  pressure of the separator is also regulated and controlled by the back pressure regulator and are safe with PSV.  These drums are equipped with a point-level sensor (LS)  and motor valve to maintain the vessels at a safety level.  Also, the temperature and pressure of the tanks are measurable by means of the temperature transmitter and  pressure gauge. The final reaction effluent stream containing a greater amount of propylene from the serial reactor  3 are supplied to the drum No.250. In addition, a flash drum (drum No.170) has been considered for  thermodynamical investigations with a total volume of 1.565 liter. It is possible that the products stream of parallel  reactor II be transferred directly to the drum by opening valve No. 102  and  closing valve No.170. The two vessels  are equipped with the level transmitters which provide a precision level measurement for a wide variety. All the  pressures, temperatures and levels of the drums are visible on the HMI. Figure 3 shows the both type of described  flash drums.   Figure 3. The photograph of flash drums and their equipments As was stated, this device has been termed a programmable automation controller PLC to establish a safe and  reliable operating condition. In this control system, a programmable computer receives input signals from the  equipment, processes this information using the structure and rules entered into the program and then it controls  outputs that operate equipment. The PLC and the safety system check the process interlock which can inform  operator at bad condition or in the emergency state automatically by activating the ESD (Emergency Shut Down).  All control and measuring commands are sent and received with Analog (4-20 mA) or digital signal and are  processed with PLC System. The measuring value such as all temperatures, pressures, feed flow rate, Product  level, Run/Stop of the Pump and other control parameters are shown on the HMI.  Figure 4.  Heater control station, PLC control Two control panels have been provided for this system (fig.4). By means of the power and heater control station, the  temperature of heaters and pre-heaters are controllable with a precise PID control loop. This panel is comprised of  19 controllers with a major key of electricity supplier and electrical fuses of equipments and SSRs (Solid State  Relay). The PLC control panel includes the instruments and PLC modules to handle multiple inputs and output  commands of the system. Also, a UPS (uninterruptible power supply) has been considered to provide emergency  power for PLC control panel in case of an electrical failure.