Reliability Analysis For Petrochemical Plants

Transcription

1 Reliability Analysis For Petrochemical Plants Itthipol Nakamanuruck, Vichai Rungreunganun, and Sompoap Talabgaew Abstract One important issue in creating a Preventive Maintenance (PM) plan is considering equipments that affect the overall reliability of the production system. At present, the Optimal Cycle Time that Maintenance Engineers regularly use for maintaining machines or equipment is the maintenance cycle time stated in the manual. Preventive maintenance is mainly based on time, which may not coincide with the equipment that affects the overall reliability of the production process. Thus, this project will aim to find the reliability of the refinery process of the refinery plants study case to analyze the subsystems that affect the overall reliability of the system. This will cause for the preventive maintenance plan of the production process to have the highest efficiency. Keywords petrochemical plants, preventive maintenance and reliability engineering. D I. INTRODUCTION URING 00 to 0, two types of equipment failures were found in a model refinery plant in Rayong province: Instrumental and Mechanical. The frequency of failure is up to times, in which statistics claim that failure of equipment can cause up to,,0 baht in maintenance cost. In addition, there are still no suitable maintenance plans available. At present, the method that is used regularly by Maintenance Engineers is the maintenance cycle time as stated in the manual. The reliability of the subsystems and the overall system is unknown, making the maintenance plan that is consistent with the reliability of the system also unknown. The objective of this research is to find the reliability of the subsystems to increase the efficiency in preventive maintenance of model refinery plants. II. LITERATURE OVERVIEW Reliability is the probability in which engineering parts or system can fully function under certain conditions and within the operating time interval [], []. This definition is applied to the reliability in many sections of several industries [], such as the Mixed Integer Programming method to find the maximum profit from machine maintenance in Hydroalkaline (HAD) petrochemical plants. The maximum profit is calculated from the availability value, which is derived from the Reliability Block Diagram (RBD) of the petrochemical Itthipol Nakamanuruck, Department of Industrial Engineering. Faculty of Engineering / King Mongkut s University of Technology North Bangkok, Thailand. itthipol.n@gmail.com. Vichai Rungreunganun,. Department of Industrial Engineering. Faculty of Engineering / King Mongkut s University of Technology North Bangkok, Thailand. r_vichai@yahoo.com. Sompoap Talabgaew, Department of Teacher Training in Mechanical Engineer / King Mongkut s University of Technology North Bangkok, Bangkok Thailand. sptg@kmutnb.ac.th. process []. The optical time to maintain the complex electric current system is then found. The concept is that as these types of systems have a multistate function system, there is continuous effect from equipment failure, so individual maintenance cannot be applied. The damage rate model is then developed from the probability of the damage occurrence and estimating the times that damage may occur. The expense ratio from the systems that were damaged and the maintenance costs were then calculated [5]. The pump, compressor, or blades with failures that make them unable to function would create many future costs; including production opportunity loss, repairing or replacing machine costs, planned maintenance costs, and so on. On the other hand, the benefits are also considered since if the types of equipment have high reliability and can operate continuously, the factory would be able to gain production profit. This is done by applying the Weibull and Exponential equations to find the equipment damage rate []. The Monte Carlo method is also used to randomly simulate the amount of times that the parts of the wind power plant is expected to be damaged, by creating an equation that shows the inverse relationship between the reliability and the useful life of equipment, called the Proportional Age Set Back (PAS) model. The deterioration of the blades from uncertain environment is studied, and the wind speed is analyzed to find the probability and deterioration rate of blades in the past to build a reliability model. III. PROCEDURE. Study refinery systems of model oil refineries The refinery system of model oil refineries can be separated into main sections, in which each section has its own Equivalent Distillation Capacity (EDC). This research focuses on the two sections with maximum EDC value, which are the Hydrocracker Unit (HCU) and Hydrocracker Unit (). These two units are in charge of splitting molecules with catalyst by using Hydrogen, with the operation in series as seen in Fig.. WD and HW HCU Products Fig. Diagram of Hydrocracker Unit (HCU) and Hydrocracker Unit () From Fig. the raw materials used in HCU are Waxy Distillate (WD) and Hydrowax (HW). The objective of this unit is to improve the quality of crude oil by converting Heavy Vacuum Oil from the High Vacuum Unit (HVU), into Light Vacuum Oil by using Hydrogen as the reactant to eliminate Sulfur and Nitrogen. However, this reaction will generate Hydrogen Sulfide (H S) and Ammonia (NH ), which is an exothermic reaction. The recycled gas will be injected at low temperatures between the levels of the reactor to control 5

2 the temperature of the system. The HCU flowchart can be seen in Fig. and for Fig. the HCU functional flowchart can be separated into Feed, Fresh gas, Recycle gas, Reactor, Hot High Pressure Separator (HHPS), Cool High Pressure Separator (CHPS), Hot Low Pressure Separator (HLPS), Make up water, Cool Low Pressure Separator (CLPS) and ADIP Absorption. As for, the objective is to convert the crude oil obtained from HCU by using fractional distillation at different temperatures. The products achieved consist of Liquefied Petroleum (LPG), Light naphtha, Heavy naphtha, Kerosene, oils and Hydrowax. The Hydrowax gained is not applicable, and would be sent back to HCU to improve the quality once again. The flowchart is shown in Fig. and for Fig. 5 the functional flowchart is separated into feed, Hydrocracker main fractionators and Side strippers. Hydrogen Fig. Hydrocracker Unit (HCU) flowchart Recycle CHPS Make up ADIP Ab LPG From the operating procedures of the Hydrocracker Unit (HCU) and Hydrocracker Unit (), the reliability of both systems can be found by converting the flowchart and functional flowchart to Reliability Block Diagram (RBD), while following the second research procedure, which is to choose machines that are significant to the HCU and system. However, for complex systems that operate continuously and every part affects the next procedure, or as called as Multi State Function, the specification of equipment significance is not only for one individual part, but rather the entire operation that is connected and affected continuously [7], []. Equipment failure will have an impact on the operation of HCU and systems, which in turn would cause loss in revenue. Thus, maintenance of these pieces of equipment is necessary, and additional maintenance cost is included. From Fig. it can be seen that HCU and is connected in series, so the reliability can be found as Equation (). R R R () S HCU From the above equation, in calculating the reliability of HCU (R HCU ) and (R ), the RBD of each process must be written first in order to find the relation of the equipment and how they are connected. In this research, only the main equipment will be focused as they are significant to the production process and cannot do without. The following section will show how to find the RBD of HCU and.. Study the reliability of the system. Finding the reliability of the Hydrocracker Unit (HCU) system Input Feed Recycle Reactor HHPS WD and HW Feed Reactor HHPS HLPS CLPS Fig. Hydrocracker Unit (HCU) functional flowchart Fig. Hydrocracker Unit () flowchart HCU Feed Hydrocracker Main Side Strippers Products Fat DIPT Fig. 5 Hydrocracker Unit () functional flowchart and reliability block diagram ADIP Ab CLPS Make up HLPS CHPS Fig. Reliability block diagram of Hydrocracker Unit (HCU) The reliability block diagram of HCU in Fig. shows the operational function blocks connected in series, as the HCU process cannot do without any of the operational functions. Each operational function will affect the following function or any other functions, thus the reliability equation of HCU can be written as follows: R R R R R RHCU Feed Fresh Recycle Reactor HHPS R R R R R CHPS MakeUp HLPS CLPS ADIPab Equation () consists of multiple operational functions, in which each function has its own reliability value. These values can be found by finding the reliability of the main equipment within each operational function, which is to separate the RBD into 0 sections. The machines in each Hydrocracker Unit (HCU) system can be specified as in Table I.. Finding the reliability of the Hydrocracker Unit () From Fig. 5 the reliability block diagram of is operated in series. The process cannot do without any of the operational functions since each operational function will affect the following function or any other functions. Therefore, the reliability equation of can be written as follows: () 5

3 R R R R () Feed HydrocrackerMF Side Strippers Similarly, the reliability of consists of multiple steps, in which each step has its own operational reliability value that the reliability can also be found. It can be done by specifying the RBD of each operation, which could be divided into sections, and the machines in each Hydrocracker Unit () is specified in Table II. TABLE I SPECIFICATION OF EQUIPMENT IN HYDROCRACKER UNIT (HCU) SYSTEM system No. ID equipment Name equipment Uptime Downtime S-70A REACTOR FRESH FEED FILTER (A)/(B) Y S-70B REACTOR FRESH FEED FILTER Y Feed S-70A REACTOR RECYCLE FEED FILTER (A) Y S-70B REACTOR RECYCLE FEED FILTER (B) Y 5 V-70 REACTOR FEED SURGE VESSEL 5 Y 5 P-70 REACTOR FEED PUMP Y V-70 F.G.COMPRESSOR ST STAGE SUCTION VESSEL 7 Y 7 K-70A FRESH GAS COMPRESSOR (A) Y K-70B FRESH GAS COMPRESSOR (B) Y K-70S FRESH GAS COMPRESSOR (S) 0 Y 0 Recycle gas K-70 RECYCLE GAS COMPRESSOR Y F-70 RECYCLE GAS FURNACE Y Reactor R-70 HCU REACTOR Y Hot High Pressure Separator (HHPS) V-70 HOT HP SEPARATOR Y Cool High Pressure Separator (CHPS) Hot Low Pressure Separator (HLPS) Make up Cool Low Pressure Separator (CLPS) ADIP Absorption M-70 STATIC MIER-HOT HP VAPOR/WASH WATER 5 Y 5 E-707 AIR/HOT HP VAPOUR Y V-70 COLD HP SEPARATOR 7 Y 7 V-70 HOT HP SEPARATOR Y V-70 WASH WATER SURGE VESSEL Y P-70A WASH WATER MAKE UP PUMP (A) 0 Y 0 P-70B WASH WATER MAKE UP PUMP (B) Y M-70 STATIC MIER-HOT LP VAPOR/ WASH WATER Y E-70 AIR/HOT LP VAPOUR Y V-705 COLD LP SEPARATOR Y P-70A WASH WATER RECYCLE PUMP (A) 5 Y 5 5 P-70B WASH WATER RECYCLE PUMP (B) Y V-7 HCU FEED GAS KO VESSEL 7 Y 7 C-7 HCU ADIP ABSORBER Y V-7 HCU TREATED GAS KO VESSEL Y system Feed Hydrocracker Main Side Strippers TABLE II SPECIFICATION OF EQUIPMENT IN HYDROCRACKER FRACTIONATOR UNIT () SYSTEM No. ID equipment Name equipment Uptime Downtime E-75A HLPL FEED/HYDROWA ECHANGER (A) 0 Y 0 E-75B HLPL FEED/HYDROWA ECHANGER (B) Y F-75 FURNACE Y C-75 MAIN FRACTIONATOR Y P-755A TCR PUMP (A) Y P-755B TCR PUMP (B) 5 Y 5 E-755 -TCR AIR COOLER Y C-75 GASOIL STRIPPER 7 Y 7 E-75 GASOIL/HYDROWA ECHANGER Y P-75A GASOIL PUMP (A) Y P-75B GASOIL PUMP (B) 0 Y 0 5 E-75A AIR/GASOIL (A) Y E-75B AIR/GASOIL (B) Y 7 C-75 KERO STRIPPER Y E-75 KERO/HYDROWA ECHANGER Y P-75A KERO PUMP (A) 5 Y 5 0 P-75B KERO PUMP (B) Y E-75A KERO RUN DOWN AIR COOLER (A) 7 Y 7 E-75B KERO RUN DOWN AIR COOLER (B) Y P-75A HYDROWA PUMP (A) Y P-75B HYDROWA PUMP (B) 50 Y 50 5 E-70 IP BFW/HYDROWA ECHANGER 5 Y 5 E-75A AIR/HYDROWA (A) 5 Y 5 7 E-75B AIR/HYDROWA (B) 5 Y 5 5

4 . Finding the reliability of the Feed system of Hydrocracker Unit (HCU) The Feed system operates between subsystems, and, in which each system is connected in series and on standby, as seen in Fig. 7. R Feed R RS 70A RS 70B RS 70A RS 70B R V 70 P70 WD and HW S-70 A S-70 A S-70 B S-70 B V-70 P-70 Fig. 7 Reliability block diagram of Feed system From Fig. 7 Feed is the process that decontaminates any contamination from the raw materials by using instruments S- 70 A/B and S-70 A/B. From there, the materials will flow to rest in V-70, before pump P-70 starts pumping into the reactor procedure. The uptime and downtime data are shown in Table. The reliability of the Feed system can be found as follows: RFeed RSubsystem RSubsystem RSubsystem Where RS 70A RS B R R RSubsystem 70 RSubsystem S70A S70B R R R Subsystem V 70 P70 Substitute the values of R Subsystem, R Subsystem and R Subsystem into the above equation, and the reliability of the Feed system becomes: System Feed Recycle gas Hot High Pressure Separator (HHPS) Hot Low Pressure Separator (HLPS) Make up Cool Low Pressure Separator (CLPS) From theory, [] ns ( t) R( t) n ( t) n s f ns ( t) ( t) n Where n 0 is the Total time (Uptime ( i ) + Downtime (Y i )) n S (t) is the Uptime (i) Substitute these values to find the reliability of the Feed system: R Feed Y Y 0 Y Y 5 5 Y5 Y TABLE III RELIABILITY EQUATION OF HYDROCRACKER UNIT (HCU) SYSTEM Reliability equation of system The reliability values of the Hydrocracker Unit (HCU) and Hydrocracker Unit () subsystems can be seen in Table III and Table IV, respectively. 5 Y Y Y Y 5 Y5 Y Y Y Y 0 Y0 Y 0 Y0 7 Y 7 0 Y Y 0 Y 0 Reactor Y Y Y Y Y 0 Y 0 Y0 Y Cool High Pressure Separator (CHPS) ADIP Absorption 5 Y Y Y 5 Y5 Y Y 5 Y 7 Y7 7 Y Y Y

5 System Feed Hydrocracker Main Side Strippers TABLE IV RELIABILITY EQUATION OF HYDROCRACKER FRACTIONATOR UNIT () SYSTEM Reliability equation of system 0 ( )( ) Y Y Y Y Y Y Y Y7 Y Y 0 Y0 Y Y Y Y Y5 Y 7 Y7 Y Y 50 Y50 5 Y5 5 Y5 5 Y5 IV. RESULTS By collecting the uptime and downtime of the equipment in the subsystems, the reliability of the subsystems can be calculated as shown in Table V. TABLE V RELIABILITY OF HYDROCRACKER UNIT (HCU) AND HYDROCRACKER FRACTIONATOR UNIT () SUBSYSTEMS Systems Subsystems Reliability Hydrocracker Unit (HCU) Hydrocracker Unit () Feed Recycle gas 0. Reactor 0. Hot High Pressure Separator (HHPS) 0.77 Cool High Pressure Separator (CHPS) 0. Hot Low Pressure Separator (HLPS) Make up 0.7 Cool Low Pressure Separator (CLPS) 0.5 ADIP Absorption 0. Feed 0.5 Hydrocracker Main 0. Side Strippers 0.5 From Table 5, when the reliability of the subsystems are found, they would be substituted into Equations () and () to find the reliability of Hydrocracker Unit (HCU) and Hydrocracker Unit () systems to be equal to 0.75 and 0.770, respectively. These values would then be substituted into Equation () to find the reliability of the main system to be 0.5. V. DISCUSSION After finding the reliability of the system as aforementioned, the results of the reliability and unreliability values achieved were arranged in ascending order, as shown in Table. TABLE VI RELIABILITY AND UNRELIABILITY VALUES SORTED INCREASINGLY Subsystem Reliability Unreliability Side Strippers Reactor ADIP Absorption Feed Recycle gas Hot High Pressure Separator (HHPS) Cool High Pressure Separator (CHPS) Cool Low Pressure Separator (CLPS) Feed Hydrocracker Main Hot Low Pressure Separator (HLPS) Make up 0 From Table, the reliability and unreliability values of the, Side strippers, Reactor, ADIP Absorption, Feed, Recycle gas, Hot High Pressure Separator (HHPS), Cool High Pressure Separator (CHPS), Cool Low Pressure Separator (CLPS), Feed, Hydrocracker Main, Hot Low Pressure Separator (HLPS) and Make up subsystems are shown in ascending order, respectively. These values show that preventive maintenance following the manual may not be suitable as there is still deterioration in the instruments, which will cause for higher expenses in corrective maintenance. Thus, the improvement of the instruments should be considered sequentially, to improve the preventive maintenance plan to have higher efficiency. VI. CONCLUSION From the analysis to find the reliability of the model refinery plant in Rayong province, in which the systems are chosen by using the equivalent distillation capacity as the criteria, the research models chosen by the researchers are Hydrocracker Unit (HCU) and Hydrocracker Unit () systems. The data used in this study is collected from 00 to 5

6 0, which includes the uptime and downtime of the equipment in the system to find the reliability of the instruments and system. This will cause the reliability of Hydrocracker Unit (HCU) and Hydrocracker Unit () systems to be 0.75 and 0.770, respectively. This in turn causes the reliability of the main system to be 0.5. This will lead to an improvement of preventive maintenance plans of model plants in the future. REFERENCES [] M. Rausand and A. Høyland. System Reliability Theory : model, statistical, method, and applications., nd ed. New York : John Wiley and Sons Inc., 00. [] Sompoap Talabgaew. Systems Reliability and Maintenance., nd.ed Bangkok : Academic Printing Center, King Mongkut s University of Technology North Bangkok, 007 [] H.D. Goel, J Grievink, P.M. Herder and M.P.C. Weijnen, Integrating reliability optimization into chemical process synthesis., Reliability engineering and system safety, vol 7, pp 7 5, December 00. [] D. Louit, R. Pascual and D. Banjevic, Optimal interval for major maintenance actions in electricity distribution networks., Electrical power and energy systems, vol, pp 0, September 00. [5] D. Ghosh and S. Roy, Maintenance optimization using probabilistic cost benefit analysis., Journal of loss revention in the process industries, vol, pp. 0 07, July 00. [] S. Carlos, A. Sanchez, S. Martorell and I. Marton, Onshore wind farms maintenance optimization using a stochastic model., Mathematical and computer modelling, vol 57, pp. -0, April 0. [7] M. Khojastepour, B. Aazhang and A. Sabharwal, Cut-set Theorems for Multi-state Networks., IEEE Transactions on Information Theory, 00 [] W. Yeh, A Fast Algorithm for Searching All Multi-State Minimal Cuts., IEEE Transactions on Reliability, vol 57, pp. 5-5, December 00 57

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