CONTROL and OPERATIONS

Transcription

1 CONTROL and OPERATIONS 1.0 OVERVIEW OF OPERATIONS The APTAC is an adiabatic reaction calorimeter capable of operating at pressures up to 2000 psia and temperatures to C. The machine is fully automated and is operated by an easy to use control program operating under Windows. Reactions are carried out in a small spherical flask which can be constructed of various materials, including glass, titanium, stainless steel and tantalum. The reaction vessel can vary in volume and mass, depending on the chemical reaction under study and the expected maximum rates of self-heating and pressure generation. Generally, most reactions are carried out in a 2-1/2 titanium vessel with a wall thickness of about 0.02 and a mass of about 30 g. The reaction vessel is prevented from bursting due to internal pressure generation by injecting nitrogen around the vessel at a rate sufficient to keep the pressure differential across the wall of the testing vessel close to zero. Figure 1.0.a shows the general plumbing schematic for the APTAC. The machine is easy to use. A series of wizards lead the operator through the experimental setup procedures. It is impossible to start an experiment without first completing all the necessary data input steps. The program is launched by double clicking on the APTAC desktop icon. A screen as shown in figure 1.0.b below is displayed. The three oval icons in blue, gray and green are used by the operator to display the status of the machine, to conduct manual operations on portions of the machine and to set up an experiment. When the initial screen is brought up by double clicking on the APTAC desktop icon, the machine will be in the display mode. Different displays can be shown on the screen by clicking on one of the menu items in the left hand panel. For instance, clicking on COMPONENT STATUS will display the panel shown in figure 1.0.c, where the status of the reaction vessel, heaters, containment vessel and valves is shown. Clicking on the 11/09 APTAC 264 Operating Manual 1

2 Figure 1.0.a. THE APTAC CALORIMETER Diagram showing general layout and plumbing P Tcpls Drop-out pot P 1 Single shot Injection The APTAC Calorimeter Vac N2 Tcpls Magnadrive stirrer Relief valve P 3 P 2 7 Exhaust 5 Figure 1.0.b Initial screen display on starting the APTAC control program. 11/09 APTAC 264 Operating Manual 2

3 Figure 1.0.c. Component Status Display 11/09 APTAC 264 Operating Manual 3

4 Clicking on the green oval and then on the Heat Mode menu item in the left hand panel will show the wizard in figure 1.0.d. This wizard will lead the operator through the steps necessary to specify the mode of heating and the start and end temperatures. Figure 1.0.d. Heating Scheme Wizard 1.1 HEATING STRATEGIES Various initial heating strategies for the sample may be used, including: Heat-Wait-Search. The sample is heated in small steps with an exotherm search at each step. When an exotherm is detected the heating mode shifts to adiabatic. Heat-Soak-Search. This strategy is used to hold the sample isothermal at some elevated temperature until either an exotherm is detected or a pre-set time limit is exceeded. Heat ramp (By fixed, constant temperature difference). The sample is heated by keeping a constant temperature differential between the testing vessel and the heaters., thus simulating fire exposure to a reactor or storage tank. No exotherm detection occurs so that heat is input to the reactor by the heaters even during an exotherm. 11/09 APTAC 264 Operating Manual 4

5 Heat ramp (By rate). reached. The sample is heated at some specified rate until an end temperature is Heat ramp (by rate with exotherm detection). The sample is heated at some specified rate until an exotherm is detected whereupon the system reverts to an adiabatic mode. Isothermal. For this mode, the sample is heated to the required temperature at the stated heating rate and held there until the time limit is exceeded. The sample is then cooled down. No exotherm detection occurs. There are two type of tests which may be run in the APTAC, either closed or vented vessel, and these may be further subdivided depending on whether or not a liquid or gas sample is to be injected into the reaction vessel at some point in the experiment. In addition, the operator may choose to have the machine control the adiabaticity of the sample using either the reaction vessel wall thermocouple or the thermocouple inside the reaction vessel and in direct contact with the sample. 1.2 VENTED TESTS. The APTAC can also be used for conducting vented tests. A simple method against an applied backpressure is available on the basic APTAC. A controlled method which more realistically simulates a relief valve opening, is available as part of the APTAC Plus system. In the simple method, material is vented into an external vessel which has been pressurized to the vent set pressure. It is possible to distinguish between a tempered, gassy and hybrid system and to measure the maximum rates of selfheating and gas production at the vent set pressure and throughout the vent period. 11/09 APTAC 264 Operating Manual 5

6 In the controlled vent mode, available on the APTAC Plus system, material is vented into a pre-evacuated vessel which is continuously weighed so that the mass flux from the vessel is obtained at the vent set pressure. In addition, permanent gases are separated from the vapor or condensable and led to a separate vessel through a second flow control valve, thus giving the rate of gas production also. 1.3 CHOOSING EITHER THE WALL OR SAMPLE THERMOCOUPLE. For most closed vessel tests, the preferred thermocouple is the one in direct contact with the liquid sample. This thermocouple (inconel sheathed 0.02 diameter) will accurately measure an exotherm up to several hundred degrees per minute. However, it is sometimes desirable to use the wall thermocouple to measure the sample temperature and control the temperature of the heated space surrounding the reaction vessel. Two special situations come to mind: 1. Closed Vessel Tests. If a particular sample is known to have a large adiabatic temperature rise, or if the maximum rate of self-heating in a low thermal inertia reaction vessel would exceed the capabilities of the APTAC to accurately track the exotherm, then the exotherm should be studied in a smaller testing vessel. This would effectively increase the Φ factor for the experiment and thus decrease the peak heating rate and the adiabatic temperature rise. However, because the sample thermal mass is now much closer in value to that of the testing vessel, a significant fraction of the reaction heat will be lost to the testing vessel from the sample. Since it is the system (the sample plus the testing vessel) which must be kept adiabatic, the measuring thermocouple can be strapped to the outside of the reaction testing vessel. Care must be taken to ensure that no large deviation between the wall thermocouple and the inside sample thermocouple exists during the experiment by carefully choosing the ratio of the sample mass and the testing vessel mass. Thinner walled (0.01 ) testing vessels and smaller diameter testing vessels with thicker walls will be available from Arthur D. Little. Glass testing vessels are also available for those tests requiring particular inertness or resistance to corrosion. 11/09 APTAC 264 Operating Manual 6

7 In addition, if corrosive reactants (corrosive to the sheathing material of the thermocouple) are being studied, it may be desirable to remove the sample thermocouple from the liquid and use the wall thermocouple as the control. The upper limit of tracking the exotherm will, in this case, be determined by the thickness and conductivity of the testing vessel wall. 2. Vented Tests. During a vented test the liquid level in the reaction vessel falls throughout the venting period. Eventually, if sufficient material has been vented, the tip of the sample measuring thermocouple may become exposed. During the transition period between measuring liquid and vapor temperature the signal from the thermocouple becomes very noisy as the swirling liquid moves around the vessel and wets the thermocouple at the boundary of the liquid and vapor. Although the absolute temperature fluctuations may be only a few degrees, the rate of fluctuation is such that the heat rate plot can look very noisy. If the temperature fluctuations are larger, then temperature control of the heated space becomes uncertain. Since, during a vented test, the maximum self-heat rates are limited (and thus the temperature of the inside and outside wall are to all intents and purposes equal), it is feasible to use the wall thermocouple to measure the sample and control the heated space temperature, thus overcoming the problem. 11/09 APTAC 264 Operating Manual 7

8 1.4 CALIBRATING THE WALL THERMOCOUPLE. The wall thermocouple is automatically calibrated during a standard calibration test. The operator must ensure that the thermocouple is in good thermal contact with the wall surface of the testing vessel and that it is not likely to come loose during the test. Calibration of both wall and sample thermocouples is done using an empty, clean standard reaction vessel. Nitrogen gas is used to initially pressurize the vessel to about 500 psia (or some other pressure of the operator s choice). The machine will then automatically generate and store a table of offset values between the nitrogen temperature and the sample and wall temperatures in 50 degree increments. These values are subsequently used by the control program during a normal experimental run. 1.5 SAMPLE INJECTIONS Single-Shot Injections A single liquid sample may be automatically injected into the reaction vessel during an experiment by a pressurized sample injection vessel (the single-shot injection system). The liquid is injected at a reaction vessel temperature which is set by the operator at the beginning of the test. Figure 1.0.e shows the plumbing scheme for the APTAC Plus system and illustrates both the one-shot and syringe pump injection systems High Pressure Syringe Pump Injections In the APTAC Plus system, one or two liquid samples may be automatically injected into the reaction vessel. The liquids are injected at reaction vessel temperatures which are set by the operator at the beginning of the test. The temperatures do not have to be identical. Flow control of the injected liquids is precise and accurate and it is possible to inject liquids against a backpressure of up to 1500 psia. Liquefied gases such as ammonia, butadiene or ethylene oxide can be accurately metered using the syringe pump. The single-shot injection system cannot be used to inject such materials. 11/09 APTAC 264 Operating Manual 8

9 1.5.3 Gas Injection This option is only available on the APTAC Plus System. A gas cylinder is attached to the gas inlet port (valve 11), as shown in figure 1.e, but the control program has no control over the gas flow rate into the reaction vessel. The operator must therefore pre-adjust the flow using an appropriate needle valve and pressure regulator. The program will open the gas inlet ball valve at the required sample temperature and shut the ball valve when the pressure reaches the correct level. The operator must enter the target pressure of the injected gas. 11/09 APTAC 264 Operating Manual 9

10 Figure 1.0.e. THE APTAC PLUS SYSTEM Diagram showing general layout and plumbing P High pressure syringe pump 12 Sample 1 Sample 2 Solvent Waste Vent gas flow control P 6 P 5 Gas inlet P 4 Condensate 9 Tcpls Drop-out pot P 1 Single shot Injection gas Scales The APTAC Calorimeter Vac N2 Tcpls Magnadrive stirrer Relief valve P 3 P 2 7 Exhaust 5 11/09 APTAC 264 Operating Manual 10

11 2.0 SUMMARY OF SAFETY FEATURES 2.1 TEMPERATURE AND HEATERS. Because the total power available to the heaters is high (approximately 5 KW) meltdown of the heaters can occur very rapidly if an inadvertent fault were to happen such as a computer malfunction. There are therefore several different protective elements in the hardware and the software to minimize the possibility of heater destruction. Use of these features has greatly extended the life of the heaters The power delivered to the heaters is limited by a software control parameter which is related to the temperature and rate of heating of the sample. If the actual power demand is greater than the demand expected by the control system, the program will shut down the heaters and end the test. An upper temperature limit on the heaters is set by an operator controlled parameter during the test setup. The heaters will not exceed this value even if an exotherm is in progress. The main heater power relay is under the control of a software switch which may also be operated by hitting the Stop button displayed on the CRT. This gives rapid power off under the direction of an operator when the apparatus is being manually controlled. There are separate, manually set, temperature cut offs for the heaters. Outputs from independent thermocouples are sent directly to the main power relay which is switched off if the temperature exceeds the upper limit for the heaters. If the power to the amplifiers is lost or any of the control thermocouples fail, the computer can detect this condition and immediately shuts off power to the heaters and ends the test. 11/09 APTAC 264 Operating Manual 11

12 2.2 PRESSURE. Automatic shutdown or other protective actions and warnings will occur if the following conditions prevail: If the pressure difference between the reaction and containment vessels exceeds a preset value. If the absolute pressure in the containment vessel exceeds 2000 psia. If the absolute pressure in the containment vessel exceeds the maximum test pressure set by the operator. If the pressure difference across the reaction vessel wall exceeds a preset value and the containment vessel pressure is greater than the reaction vessel pressure, then the computer will open the bypass valve connecting the two vessels in order to prevent crushing of the thin walled reaction testing vessel. The nitrogen supply pressure is intermittently monitored and checked against the operator specified maximum test pressure. Warnings will be written to the screen but no corrective action will be taken if the supply pressure is too low. Rather, the machine will eventually detect the resulting pressure differential between the reaction vessel and the containment vessel and will shut down the test when this value exceeds the maximum tolerable value. The vacuum pump is protected by the fact that the computer will not open the vacuum valve if a pressure greater than 20 psia exists in the line upstream of the valve. The pressure containment vessel is further protected by a safety relief valve and a rupture disc. The single shot vessel is protected by a safety release valve set at 1000 psig. 11/09 APTAC 264 Operating Manual 12

13 2.3 SPILLS AND LEAKS All sample containers associated with the syringe pump and the controlled vent system are contained in a vented cabinet. The calorimeter assembly, high pressure tubing and valves and the single-shot injection testing vessel are contained in a second cabinet. Both of these cabinets are connected to a vent duct and an exhaust fan. If the apparatus is operated in the general laboratory workspace the exhaust can be ducted to a hood. If the apparatus is placed in a walk-in hood then the exhaust can be blown directly to the hood. Spills are thus contained in the cabinets and exposure of personnel to vapors is minimized. In addition, the area directly behind the head of the pressure vessel is vented so that when removing the sample testing vessels from the apparatus, exposure to vapors is again minimized. The use of nonporous, chemically resistant, ceramic insulation in the pressure containment vessel also makes clean-up after a leak or reaction vessel breakage much easier. 2.4 GENERAL A number of other features enhance the overall safety and ease of use of the apparatus, including A watch-dog timer ensures that the machine will safely shut down in the event of a computer failure. The computer control program outputs a continuous, timed, series of pulses to the watch-dog timer. If the pulse stream is interrupted, the power to the heaters and valves is automatically shut off. A mechanized head lift raises and lowers the heavy, top head assembly. Valve position indicators give positive identification of the position of each valve. The control software will not carry out some operations if valves are incorrectly positioned. Cabinet door locks are under computer supervision to minimize potential personnel exposure to chemicals. 11/09 APTAC 264 Operating Manual 13

14 3.0 TUTORIAL. HOW TO RUN AN EXPERIMENT in 10 easy steps 3.1 STEP 1. Start up the machine Make sure the power cable is plugged in and the power to the machine is on. The far right hand indicator light (green) should be on. Turn on the power switch in the electronics cabinet (the center indicator light should come on). Turn on the heater power switches in the electronics cabinet. Make sure that the air-operated ball valves have about 80 psia source pressure. Boot up the computer and start the control program by clicking on the APTAC desktop icon. The power to the heaters and valves can now be switched by pressing the power on button in the top right hand corner of the APTAC (the round, white button) when the control program requests the action. If the power button is already on then press the power off button first, followed by the on button. At this point you should have heard the air-operated ball valves switch and the two green indicator lights next to the power on button should be lighted. The third green indicator light will come on when the control program switches the power to the heaters. This can only occur if the cabinet doors are closed and locked and either an experiment is being run or the heaters are being controlled under the Manual Operations mode. 3.2 STEP 2. Attach the reaction vessel to the machine. The reaction vessel usually would contain some or all of the ingredients necessary to run the test. Record the mass of the testing vessel, the stirrer bar and the reactants in the testing vessel. Use a grafoil ferrule and a titanium nut to attach the vessel to the swagelok fitting. A torque wrench would be useful for tightening the nut in a consistent manner. Lower the head and attach the C clamps. 11/09 APTAC 264 Operating Manual 14

15 If injections are to be made during the test, load the necessary samples into the sample containers (for syringe injections using the APTAC Plus) or load the sample to be injected into the 1-shot injection testing vessel. 3.3 STEP 3. Conduct any necessary manual operations. Choose the desired operation from the Setup menu by clicking on the gray oval. e.g. if an injection is to be made during the test using the syringe pump, then the pump has to be primed correctly in order to obtain the most accurate results. (See section Manual Operations for further details). 3.4 STEP 4. Open an experiment setup file. Click on the File menu and scroll to open to select a previously run test or new to open a blank file. 3.5 STEP 5. Set up the experiment (See section 10.4) Click on the green oval and select in turn each of the menus displayed in the left hand panel of the screen. The Wizards will lead you through each step of the experiment setup process. Note that as each of the menus is completed a small tick mark appears to the left of the menu. Each of the menu items must have the tick mark before proceeding to the last of the menu items (Start run). See description of Menus for details of the information which must be entered under Experiment (section 10.4). 11/09 APTAC 264 Operating Manual 15

16 3.5.1 Closed Vessel See section 5.0 for more information on closed vessel tests. Usually, the materials or reactants to be tested are put into the reaction vessel prior to the beginning of a closed vessel experiment and this is often the simplest and easiest way to start an experiment. However, it is sometimes necessary to add a component material to the reaction vessel after it is attached to the apparatus or even after the test has started. Such instances arise for example if a catalyst or a suppression agent has to be added when the reaction vessel contents are at elevated temperature and pressure. Another example would be the necessity of adding a gas to the vessel, a procedure which obviously cannot be achieved by pre-loading the testing vessel prior to its attachment to the apparatus. Using the basic APTAC, the operator has only one choice for addition of sample and that is via the single-shot injection testing vessel. The APTAC Plus system also allows injections of up to two additional liquid samples via a high pressure syringe pump and the automatic injection of a single gas Calibration Test. See section 4.0 for more information on calibration tests. A calibration test must be done any time that the sample, testing vessel wall or nitrogen space thermocouples are replaced. In addition it is recommended that a calibration be done periodically at about the frequency of once in every ten tests. A calibration test is very simple to run using an empty testing vessel and can be done overnight so that the machine will be ready for use by the following morning Single-Shot Injection (See section ) The reactant to be injected should be placed in the cleaned, single-shot vessel and attached to the apparatus. Do not try to inject more than about 20 mls of reactant using a 50 ml injection vessel. The injection vessel will be pressurized automatically during the experiment to a pressure determined by the control program which will depend on: 11/09 APTAC 264 Operating Manual 16

17 the volume to be injected the volume of material in the reaction vessel at the time of the injection the volume of the reaction vessel the volume of the injection vessel the pressure in the reaction vessel at the time of injection. Therefore, as the volume to be injected increases, the available head space for the pressurizing gas decreases. The upper limit for pressure in the injection vessel is 1000 psia Syringe Injection. Syringe pump injections are only available with the APTAC Plus system. Prior to starting this type of test the necessary samples must be placed into the sample containers and the syringe pump must be set up properly. See Syringe Pump Setup in section Gas Injection. Attach the gas cylinder to the inlet port (of valve 11--see figure 1.0.e). The control program has no control over the gas flow rate into the reaction vessel, so the operator must control the flow using an appropriate needle valve and pressure regulator. This means that the operator should be present when the control program reaches the point where the gas injection starts, unless the flow rate has been pre-adjusted to some suitable small rate. The program will shut the ball valve when the pressure reaches the correct level. (Only with the APTAC Plus system). It is recommended that a non-return valve is installed on the line when gas injection is used in order to prevent backflow of materials from the reaction vessel. (See section 6.3.3) Vented Vessel See section 7.0 for more information on vented tests 11/09 APTAC 264 Operating Manual 17

18 Simple Vent In the simple venting mode, the reaction vessel is vented at a pre-determined set pressure into a 500 ml drop-out pot. If the vent vessel outlet valve (valve 7...see Fig. 1.0.a) is kept open throughout the test then at the point when the vent valve is opened, the pressure in the vent vessel will be equal to the pressure in the reaction vessel and there will be a seamless change in the rate of pressure rise of the sample due to the vent opening. Moreover, because valve 7 is open, the control program will continuously exhaust the vent vessel to keep it at the vent set pressure. Therefore, if the pressure drop down the tubing is small, the reaction vessel will be venting at a constant pressure. If, on the other hand, the vent vessel outlet valve is closed, the reaction vessel will exhaust into the closed vent vessel and the pressure will rise if the reaction is a gassy one. The operator has the ability to change the pressure at which valve 7 will be closed. If he chooses a pressure setting lower than the vent set pressure, the reaction vessel will blowdown to that pressure when the vent opens Controlled Vent Controlled vent tests are only available with the APTAC Plus system. See section 7.2 for more information on controlled vent tests. In the controlled venting mode, the reaction vessel is vented through a ball valve and a flow control valve at a pre-determined set pressure into a condenser which sits on a set of scales. The condenser is controlled at a fixed set pressure via a small flow control valve. Any permanent gases evolved during the venting process are vented into the gas collection bottle via the condenser and flow valves. The condenser and gas collection bottle can be automatically pre-evacuated at the start of the test and as part of the test procedure. Venting will end when the rate of temperature rise in the sample testing vessel is below the exotherm detection level and the mass rate of condensate evolution is less than 0.01 g/min. In addition, if the reaction vessel pressure falls below the set pressure by more than the Pressure Difference to End Venting, the venting will also end. 11/09 APTAC 264 Operating Manual 18

19 3.6 STEP 6. Start Run Now click on the Start Run menu item and follow the directions in the wizard. At this point the operator is given the choice of leak checking the vessel prior to the start of the test. It is recommended that this choice be accepted since it can potentially save much time and aggravation due to a leaky reaction vessel. Be careful to enter the correct strength of reaction vessel (the maximum pressure difference which can be tolerated by the testing vessel). The containment vessel will then be pressurized to half this value plus the initial pressure in the reaction vessel. The program will wait for thirty minutes to detect any pressure rise in the reaction testing vessel and any significant pressure drop in the containment vessel. If leaks are detected, the machine will not continue with the test unless the leak control parameters are altered or the leak is stopped. Usually the operator should depressurize the vessel, remove the C clamps, tighten the reaction vessel on the swagelok fitting and start the test again. 3.7 STEP 7. Displaying data during the Run. (See section 8.2) Simply point and click on blue Display Icon to show the following menu of available data displays. You will note that data plotted as a function of temperature is displayed on a reciprocal temperature axis in C. 11/09 APTAC 264 Operating Manual 19

20 * Equipment Diagrams * Experiment Graphs * Temperature - Time * Pressure - Time * Pressure - Temperature * Heat Rate - Temperature * Pressure Rate - Temperature * Temperature Difference - Time * Pressure Difference - Time * Scale Weight - Time * Condenser Pressure - Time * Gas Pressure - Time * Component Status Shows the status of the valves and the instantaneous temperatures and pressures in various parts of the apparatus, as well as the rates of temperature and pressure rise. * Equipment Settings Shows the status of the heaters and flow control valves and also the control signals sent to the heaters and valves. 11/09 APTAC 264 Operating Manual 20

21 * Logged Data This screen displays the historical data from the test in a tabular format. The operator can traverse the data by clicking on the scroll bar at the bottom of the screen. * Clear Screen 3.8 STEP 8. Stopping the Run. If the operator wishes to stop the run for any reason it may be done by clicking on the large Stop button in the upper right hand corner of the display. However, if this option is taken, the data logging into the file will stop and therefore the cooldown data will not be logged. In addition, the machine will not control the depressurizing of the containment vessel as the reaction vessel cools down and as the pressure decreases. A preferred method of interrupting the test or ending it prematurely is to right click the mouse to display a small subset of the original test setup parameters. New values for these data may be entered at any time during the test. Therefore, if the operator types in a new value for the End Test Temperature which is lower than the current sample temperature, the test will immediately end but the program will retain control over the depressurization and will write the cooldown data into the file. The stop sign will remain on the screen until the cooldown temperature has been reached. 3.9 STEP 9. Data Analysis (See section 8.5) When the Stop sign is no longer present on the screen, the operator can place the mouse pointer on the Reports menu and open up any file containing experimental data (all experimental data files have the extension *.rpt). Any notes which need to be added to the file may be typed in under the edit item on the menu. Clicking on preferences will bring up a wizard which allows the operator to choose which plots are required in the report and whether or not the data should be printed out in a tabular format. See also section 8.0 Report Generation STEP 10. Cleanup after the test 11/09 APTAC 264 Operating Manual 21

22 The following items will need to be cleaned after a test, depending on what portions of the apparatus were used for the experiment. Note that under the gray SETUP icon there is a menu item called Clean Apparatus. This item is not currently active, but in the near future an updated software package will incorporate an automated procedure for cleaning the lines from the syringe pump to the condenser and to the single shot injection vessel. The syringe pump, the valves and lines leading to and from the pump. Fill the solvent container with a compatible solvent and pump solvent through the lines using the Manual Operations menu. The sample transducers and the lines leading to them. Be sure to replace the Teflon inserts (they are used to decrease the dead volume in the system and minimize the loss of volatile sample from the reaction vessel) The lines leading to the controlled vent system, the ball valve and flow valve associated with the vent system and the line leading to the condenser vessel. By attaching a small vessel (about 1/2 diameter x 3.5 long) to the top heater in place of a standard reaction vessel, it is possible to pump a solvent through these lines using the syringe pump. The line leading to the drop-out pot and the drop-out pot. (see the note above concerning the controlled vent system...a similar arrangement is possible) The valve and line leading to the single-shot injection vessel and the vessel itself. If a large leak occurred or the reaction vessel burst during the test, then the pressure vessel will need to be cleaned. In addition the nitrogen/exhaust line leading to the pressure vessel will also need to be flushed out. If no damage occurred to the heaters due to a burst vessel (from either the pressure pulse or from corrosive materials spilled on the heaters/thermocouples) then the pressure vessel could probably be simply flushed out with a suitable solvent without the need to remove the heaters/thermocouples and insulation. A manually operated drain valve on the base of the containment vessel is provided. 11/09 APTAC 264 Operating Manual 22

23 4.0 MANUAL OPERATIONS Clicking on the gray, oval icon will change the panel on the left hand side of the screen to gray and will display a list of four items, one of which is Manual Operations. The gray, oval icon will not be active once an experiment has started and therefore, with the current version of the software, manual operations cannot be conducted during an experiment. Under the Manual Operations item, the operator has the ability to initiate operations on specific pieces of the apparatus, although direct control over the individual valves and heaters is not, at this time, available to the operator. Any operation, once started, will result in the appearance of the large, red STOP button in the upper right hand corner of the screen. Clicking on the STOP button will prematurely and immediately stop the operation, otherwise the operation will be stopped by the control program when the correct end point has been reached. The following actions may be done under Manual Operations. 4.1 CHANGE PRESSURE This button is used for changing the pressure in a specific portion of the apparatus under computer control. The operator is not able to open or close individual valves, but can carry out certain operations on the machine by use of the manual control buttons. Clicking on change pressure will bring up a menu requesting the operator to input the part of the apparatus to which the change pressure applies and what pressure is desired. The rate of pressurization/depressurization is not a variable which can be changed by the operator and is pre-set at about 250 psi/min. 11/09 APTAC 264 Operating Manual 23

24 4.1.1 Reaction Vessel: In order to change pressure in the reaction vessel, the pressure must simultaneously change in the containment vessel. Therefore valves 1 & 7 are opened and nitrogen flow is controlled until the desired pressure is reached. Note that at the end of the pressurization period both of these valves remain open. If valve 1 needs to be closed, the change pressure button should be clicked again and the containment/simple vent button should be chosen. A pressure several psi below the current containment vessel pressure should be typed in. Valve 1 will be closed prior to bleeding out the nitrogen. As soon as the valve is closed, the operation should be stopped by clicking on the STOP button Single-Shot Injection Vessel: Valve 2 will switch and the pressure will be regulated in the single shot injection vessel. Because the volume of the single shot injection vessel is very small, good control of the pressurization and depressurization of this vessel is not possible with a very high nitrogen source pressure. Therefore the operator may wish to turn down the source supply regulator to a more manageable level. At the end of the operation, valve 2 will switch back to the containment pressure vessel Containment/Simple Vent: Pressure in the containment and simple vent vessel will be changed but the reaction vessel pressure will remain constant. Valve 1 will remain closed but valve 7 will be open. Note that if a differential pressure is required between the reaction vessel and the containment vessel, the pressure must first be changed in the reaction vessel and then in the containment vessel. 11/09 APTAC 264 Operating Manual 24

25 4.1.4 Gas Collection Vessel: The maximum pressure in this vessel is 20 psia. The vessel is pressurized from the high pressure nitrogen source supply via valves 2 and 5 and the nitrogen flow control valve. Overpressure protection is provided by virtue of the push-fit rubber stopper in the neck of the vessel. A pressure differential across the small flow control valve between the condenser and the gas collector may be established by first pressurizing the condenser (see below) followed by an adjustment to the pressure of the gas collection vessel Condenser Vessel: The pressure in the condenser may only be changed via the gas collection vessel and consequently is limited to 20 psia on the upper end. Usually, the pressure in this vessel is reduced below atmospheric. At the end of the operation, valves 2 & 5 will switch back to their normal (un-energized) positions Containment Only: The pressure in the containment vessel only will be changed. The valve leading to the reaction vessel (valve #1) will be closed during the operation and also the valve (#7) on the exit of the vent drop-out pot (the Simple Vent vessel). Thus, neither the reaction vessel nor the simple vent container will be pressurized. This operation is in contrast to the operation under where valve #7 is opened and the vent vessel is also pressurized. Therefore, if it is desired to create a pressure differential between the vent container and containment vessel, two separate operations are required. Firstly, the pressure in the both the containment and the vent vessel is raised to the desired pressure under and then a second operation is conducted where the pressure in the containment vessel only is altered to create the pressure differential. 11/09 APTAC 264 Operating Manual 25

26 It is also possible to create a differential pressure between the reaction vessel and the containment vessel or the vent vessel using a combination of the actions under 4.1.1, and PURGE Inactive at this time 4.3 LEAK CHECK The automated procedure designed to cover all portions of the apparatus is inactive at this time, although an abbreviated procedure for the reaction vessel is available as part of the start test procedure. If the operator wishes to check portions of the apparatus for leaks, a differential pressure should be created as described in the above paragraphs. After creating the differential pressure, the operator should wait a period of time for any temperature oscillations to dampen (created by the rapidly changing pressure) and then read the rate of pressure rise or fall associated with that portion of the apparatus. Very small leaks can be detected using this procedure but the operator must be prepared to wait about minutes in order to detect leaks of the order psi/min. An even longer wait time may be appropriate to detect smaller leaks and, of course, shorter wait times are required for large leaks. It is very important that the reaction vessel in particular should be leak tight and it is recommended that a leak test be conducted as part of the test procedure. A small leak from the reaction vessel during a test can have a very large effect on the test result, leading not only to loss of ingredients but also possibly to large heat losses as a result of evaporative cooling. An automated leak test can be incorporated into the test procedure if the operator requests it when starting a test. The leak test should return a value between 0.01 and psi/min. If the leak is positive, it indicates that nitrogen is leaking from the pressurized containment vessel into the reaction vessel. The only place this can occur is around the neck of the vessel where it is attached to the 1/2 Swagelok fitting. The apparatus should be de-pressurized and the head raised. The operator can then either tighten the fitting or remove the reaction vessel, inspect the neck and grafoil ferrule for damage and then replace the vessel on the fitting. A torque wrench would be a useful tool for consistent tightening of the nut. 11/09 APTAC 264 Operating Manual 26

27 4.4 OPERATE SYRINGE PUMP It is always necessary prior to the start of a test to ensure that the lines from the sample containers to the reaction vessel are filled with the liquid to be pumped during a test. The operator must accomplish this under manual operations. Also, after completion of a test, it will be necessary to pump a suitable solvent through the lines to flush out the chemicals used during the test. Liquids can be pumped from the sample containers to either the waste container or the reaction vessel. The operation is completed in two parts. Firstly, the liquid is drawn into the syringe barrel from the appropriate sample container and in a second operation, the liquid is pumped to the waste or the reaction vessel. The machine will switch the appropriate valves to accomplish the specified task. The operator must specify the diameter of the syringe barrel and the pressure rating. It is very important that these numbers are entered correctly, not only for accurate metering but also for safety. In addition, the operator must also input the volume to be delivered or pulled into the syringe and the rate of pumping or refilling. For more details on using the syringe pump, see section Syringe Pump Injections. 4.5 INJECT FROM 1-SHOT The reactant to be injected should be placed in the cleaned, single-shot vessel and attached to the apparatus. Do not try to inject more than about 20 mls of reactant using a 50 ml injection vessel. The injection vessel will be pressurized automatically during the operation to a pressure determined by the data input by the operator and the pressure which exists in the reaction vessel at the time of the injection. The upper limit for pressure in the injection vessel is 1000 psia. The operator should type in the following data: 11/09 APTAC 264 Operating Manual 27

28 The volume to be injected The volume of material currently in the reaction vessel The volume of the injection vessel The volume of the reaction vessel. The machine will immediately pressurize the injection vessel to an appropriate pressure and then switch the valves to begin the injection process. When nitrogen breakthrough is detected by the apparatus, the injection valves are closed. 4.6 INJECT GAS This option is only available on the APTAC Plus System. Attach the gas cylinder to the inlet port (of valve11). The control program has no control over the gas flow rate into the reaction vessel, so the operator must control the flow using an appropriate needle valve and pressure regulator. This means that the operator should be present when the control program reaches the point where the gas injection starts, unless the flow rate has been pre-adjusted to some suitable small rate. The program will shut the ball valve when the pressure reaches the correct level. The operator must enter the target pressure of the injected gas. 4.7 CHANGE TEMPERATURE. The operator is able to change the temperature of the environment in the containment vessel by simply specifying the desired temperature and the rate of heating. Individual operation of each heater is not available as an option. Instead, the machine will operate all heaters simultaneously to control the temperature of the nitrogen in the containment vessel at the set temperature. The cabinet doors on both the calorimeter cabinet and the APTAC Plus cabinet (if installed) must be closed prior to starting this operation, else the heaters will not be switched on. 11/09 APTAC 264 Operating Manual 28

29 4.8 CHANGE STIRRER SPEED The speed of the stirring system can be altered by typing in a new value in the Change Stirrer Speed Wizard and clicking on Finish. If the operator type in a number less than ten (rpm), the stirrer will be turned off. 4.9 TARE SCALES The scales are tared and the condensate mass reading in the Component Status display will be zeroed STOP OPERATION All current manual operations will be stopped and settings returned to default values. If the heaters are currently being controlled at a set temperature, the set point will be set to zero C and the heater power turned off. 11/09 APTAC 264 Operating Manual 29

30 5.0 CALIBRATING THE APPARATUS Calibration of the apparatus is extremely important for efficient and accurate operation of the machine. Both absolute and relative calibration of the thermocouples should be done on a regular basis. A relative calibration of the thermocouples is done to ensure that when the sample, testing vessel wall and nitrogen thermocouples are in the same temperature environment they will output the same values to the data logging system. Relative calibration is simple and easy to do and may be done overnight so that the machine is ready for use at the beginning of the day. On the other hand, absolute calibration of the thermocouples over the full temperature range of the apparatus can be tricky. Therefore, a single point absolute calibration at zero C is used and it is assumed that the thermocouple/amplifier combinations are within manufacturers specifications over the range used by the instrument. 5.1 RELATIVE CALIBRATION OF THE THERMOCOUPLES In order to minimize the potential for either positive or negative drift when the machine is in the Searching for Exotherm mode, the sample, testing vessel wall and nitrogen space thermocouples must be in close agreement when they are in the same temperature environment. An adiabatic environment within the heated space of the apparatus is maintained by controlling the temperature of the nitrogen to be exactly the same as the temperature of the sample. A small deviation between the two temperatures, especially when the self-heat rate of the sample is low, can lead to substantial errors. If the nitrogen thermocouple reads higher than the sample thermocouple at the same temperature, then the control system will turn down the heater temperature, leading to a loss of heat from the sample testing vessel and a negative drift rate. Experience has shown that at modest pressures within the containment vessel, a one degree centigrade temperature difference will lead to a drift rate of approximately 0.1 C/min. At high pressures the drift rate for the same temperature difference will be greater and at lower pressures it will be smaller because the rate of heat transfer to and from the testing vessel wall will depend on the surrounding pressure. Therefore, in order to achieve an exotherm detection level of 0.01 C/min, the thermocouples must be calibrated to within 0.1 C. 11/09 APTAC 264 Operating Manual 30

31 For elevated pressure work, calibration must be better. For this reason, the practical exotherm detection level varies with pressure. The apparatus specification for the exotherm detection level is 0.04 C/min, although this figure can be improved at low pressure and will degrade at elevated pressures Starting a relative calibration. The setup wizard for starting a calibration test is brought up by clicking on the gray oval labeled SETUP and then clicking on the CALIBRATION menu item displayed in the left hand panel. The sample, wall and nitrogen space thermocouples are calibrated using this operation. Calibration may be done using an empty testing vessel or a testing vessel containing a suitable liquid (a liquid which has no thermal activity over the temperature range which the calibration will cover and that also has a suitable vapor pressure at the high end of the range). Usually, the calibration is carried out using an empty reaction vessel which is pressurized with nitrogen gas. Clicking on the calibration menu under Setup will bring up a menu of data which the operator will need to enter prior to starting the test. These data include the starting pressure, the end temperature, the cooldown temperature, the heating rate and the upper and lower pressure band for the pressure balancing system. Generally, it is recommended that a pressure of 500 psia be chosen as the initial pressure in the vessel, although other pressures may be chosen by the operator. The starting temperature of the calibration test is always 50 C, so the operator must ensure that the containment vessel and insulation is below that temperature prior to starting a calibration. The end temperature can extend to 460 C. This temperature will ensure that the 450 C point will be measured. 11/09 APTAC 264 Operating Manual 31

32 5.1.2 Displaying the measured calibration data graphically A table of calibration offsets (the difference in temperature between the nitrogen thermocouple and the sample thermocouple at 50 degree intervals) is generated and stored. The table is subsequently used by the control program to adjust the sample thermocouple when running a standard experiment. The calibration data for the sample thermocouple may be displayed by clicking on the View menu at the top of the screen and scrolling to Calibration data. A graph of the calibration data and a table of the individual values will be displayed, as shown in figure a below. FIGURE a It may be noted that the machine cannot obtain the zero degree Celsius point nor the 500 Celsius point. Instead, the operator must manually enter the points into the calibration offset table (see next section) 11/09 APTAC 264 Operating Manual 32

33 5.1.3 Displaying and changing the calibration data The data may also be displayed and individual data points changed using the Shift-Ctrl-Left Arrow keys simultaneously when in the Display mode on the screen. This will bring up a display of default values for parameters which are used in the control program. Default Tabs 6 and 7 contain the calibration data points as shown in figure a below. The operator may need to enter corrected values for the zero and 500 degree points after a new calibration test has been completed. The values should be obtained by extrapolation of the measured calibration data and typed into the appropriate boxes in the table. Default Tabs one through five contain data which the operator should not, generally, change. Figures b illustrates some typical calibration data. The temperature and pressure during a calibration test are shown. Note that the pressure at the start of this test was 250 psia and increased throughout the test to a value of nearly 500 psia. Usually, a calibration test is conducted with an initial pressure of about 500 psia in the reaction vessel. If the operator notices any drifts in the pressure-time curve during the stable temperature periods, then the results of the test could be compromised, depending on the size of the drift. The vessel should be leak tight during the test. FIGURE a 11/09 APTAC 264 Operating Manual 33

34 Figure b Calibration test with initial presure at 450 psia PRESSURE Temperature (deg C) TEMPERATURE PRESSURE (psia) Time (mins) Figure c Temperature (deg C) Calibration test with initial presure at 450 psia showing temperature difference between sample and nitrogen. Temperature Difference Temperature Time (mins) TEMPERATURE DIFFERENCE (deg C) 11/09 APTAC 264 Operating Manual 34