Application of the Correlation Method to the Tuning of Industrial Control Schemes.

The correlation method of finding a system\u27s impulse response weights, based on the Wiener-Hopf integral, was studied for its application to the tuning of feedback, feedforward, and decoupling control elements in closed loop operation using only ordinary operating data. Also included in the work is a thorough study of actual data for eight typical stochastic disturbances taken from a refinery light ends unit. A disturbance signal typical of these actual signals was used throughout the tuning studies to make results obtained more practically meaningful. These actual signals were also used to demonstrate the desirability of differencing input and output data prior to use of the correlation method. The correlation method was applied to the tuning of feedback and decoupling controllers by using it to find the closed loop impulse response of a system\u27s output to set point changes. Given knowledge of the control structure and control elements, equations are derived which use this closed loop response to obtain the open loop impulse response. Many existing methods are available to design feedback controllers or decouplers given open loop responses. The correlation method was applied to the tuning of feedforward controllers by finding the closed loop impulse response of the system\u27s output to disturbance changes. Equations are derived which convert this closed loop response directly into an improved feedforward controller given the control structure and control elements. An approximation of the manipulated variable transfer function is also required. The equations derived for both problems are applicable to a 2 x 2 interactive process such as a distillation column with or without feedback elements, feedforward controllers, and partial or simplified decouplers. Less complex processes and/or control schemes allow the equations to be significantly simplified. A criterion called the Impulse Confidence Ratio (ICR) is proposed which when interpreted properly will allow the determination of the value of a test result. The correlation method of impulse response determination and the tuning techniques were subjected to numerous tests of robustness in the face of various non-ideal situations which might be expected to arise in real application. The tuning techniques are applied successfully to a nonlinear distillation column model

Modelling and Optimization of Sequencing of Processes for Ethylene Production

The separation process for distillation column involves handling a various multi-component mixtures. Particularly for ethylene production, we deal with a number of hydrocarbon components. The objective of this project is to separate each of these components at minimum cost without compromising the feasibility. We develop a superstructure model to determine the optimal design of distillation sequencing for ethylene production. The optimization model is formulated based on a process flowsheet superstructure representation that embeds many possible and feasible structural alternatives for the sequences of processing a multicomponent hydrocarbon mixture constituting liquid naphtha or gaseous ethane. The compositions of the feed will determine the split fractions of the components. We adopt linear mass balance reactor models for conversion of materials into desirable products and simple sharp and non-sharp separation for distillation column. Then, we will formulate a mixed-integer linear program (MILP) that involves two types of variables: (1) discrete 0–1 binary variables for selecting the tasks for an economically-optimal configuration, and (2) continuous variables for determining the optimal operating levels of flowrates into each selected tasks. Using a mathematical modelling, we compare two different feedstocks; liquid naphtha and gaseous ethane. The goal is to select a configuration of separation tasks and their corresponding units. The simulation of our model suggests a different optimal separation sequence from the typical industrial configuration due to the reconditioning of the logical and switching constraints. A more rigorous constraints that consider cost raw material cost, capital investment, production cost and profitability for the olefin production process in order to justify the feasibility of the olefin production is recommended to produce a more reliable output

Lessons learned from past accidents - The integration of human and organizational factors with the technical aspect

It is of prime importance to ensure the safety of chemical process plants due to volatile nature of the industry and drastic consequences of the accidents. A number of parameters can affect the safety of the process plants. One of the main parameters that has the influence on the safety of operations is the Human and Organizational Factors (HOF) as suggested by numbers of existing studies. Therefore, in order to enhance the safety of operations it is required to improve the HOF. These factors can be improved by an integrated approach as proposed in this work, instead looking at these factors in an isolation. A number of existing risk assessment approaches have been analysed in this work and their compliance requirements to the relevant International Standards with respect to the HOF. A new quantitative methodology “Method for Error Deduction and Incident Analysis (MEDIA)” has been developed in this work. During the development of this methodology, practicality; consistency; integration with other risk assessment techniques and efficient use of information were explicitly ensured. The MEDIA can help to integrate the HOF around the technical aspect and can prioritize the follow up actions based on risk. The quantification of this methodology is based on results of the accident analysis, that has been carried out in this work. The accidents of 25 years (1988-2012) in the Seveso establishments and that were reported to the European Commission’s Major Accident Reporting System (eMARS) have been studied. The results from the accident analysis have further used in order to learn lessons and to propose future recommendations. These recommendations are mainly aimed at further integration of the HOF and to improve the overall safety of chemical process plants. More specifically, these recommendations are addressed to the use of organizational checklist during the Hazard Identification (HAZID) study; improvement of existing eMARS reporting structure and the legal obligation towards the EU Member States to report their accidents to the European Commission

Retrofitting industrial, conventional column systems to petyluk/divided wall columns

Master'sMASTER OF ENGINEERIN

Dynamic Behaviour of Coke Drums PSVs During Blocked Outlet Condition

The maximum yield taken in an oil refinery can not exceed 70% without including Delayed Coker Unit (DCU) as part of unit operations in the refinery. This implies naturally a big attraction on investing of such a unit for refiners. However, during the past decades, there were few refiners included Coker unit in the refinery, due to the fact of its large capital investment with a high marginal profitability. On the other hand the technologies developed to operate a coker unit, involve a series of process steps that require highly trained and well experienced operators with a state of art of design to overcome all the challenges with this unit operation. Safety, as a prime factor of design and operation requires much attention in the design of this unit. Among different safety consideration in the design and operation of Coker Unit, this project thesis focuses on the dynamic behaviour of Coke Drums PSV (Process Safety Valve) relief and its interaction with Blowdown section of the unit that leads also to the PSV relief of Blowdown section with change of temperature versus time during the first 15 minutes that is considered as the time required for operators intervention. The main findings in this thesis are about the complications in the design aspects of delayed coker unit as well as the importance and role of safety of operation of this unit. It also gave me an insight of cascade relief during the upset condition in an online coke drum and the importance of a reliable piping system to handle the hydraulics as well high temperature conditions.1 yea