Volume 11, Issue 4 -

A class of functional model known as multilevel flow model (MFM) is used to represent a pilot scale heat exchanger system. MFM is effective in representing chemical process qualitatively through graphical representation, but lacks the ability to quantify the impact of successes or failures of process events, and is not able to quantitatively distinguish between steps in a goal and their contributions towards achieving the main goal. To address this issue, the MFM is converted into its equivalent fault tree (FT) model to accommodate logical sequence of events along with the needed quantifications. The FT model is then converted into Bayesian network (BN) model to facilitate updates of probabilities. Using Hugin 8.1 software, the BN model is simulated to investigate the response of the process when subjected to various faults. The results highlight the capability of the model in detecting process faults and in identifying the associated root causes, thus pointing to the potentials of the proposed strategy in modeling complex chemical processes for higher level functions in plant operations such as facilitating alarm system and fault diagnosis.

In refineries, due to the environmental pollutions, sulfur content in petroleum need be reduced. The incineration process is used for sulfur recovery system which is not friendly process to the environment and needs high temperature. This actual process exhaust high amount of SO 2 from the incinerator stack to the environment. The Claus process is the best method to recover sulfur from acid gases that contain hydrogen sulfide. The particular reaction for sulfur removal from sour gas is hydrogen sulfide (H 2 S) sulfur dioxide (SO 2 ) reformation (2H 2 S+O 2 =S 2 +2H 2 O). The aim of this study is to get a simulation that is suitable for the characterization of sulfur recovery units. The experimental design for this study was collected from a petroleum refinery located in Iran. This experimental relation supports us to gather with definite consistency that is normally not available online for such process. Aspen HYSYS v8.8 software was used to simulate the Claus process by reactors and component splitters. The result shows the complete conversion of sour gas to product. The simulation protects the environmental impact by SO 2 emission. This behavior can be reproduced by this HYSYS design very well. It was found that the BURNAIR feed composition and molar flow is the only factors which can affect the hydrogen sulfide conversion. The sulfur mole fraction increased only in the range of 0.94 to 0.98 by increasing N 2 from 0.7 to 0.9.

In this paper, benchmark simulation model no.1 (BSM1) of an activated sludge process is used to evaluate various control strategies. Control configurations such as feedback control and feed-forward plus feedback (FF-FB) control are applied and compared with respect to effluent discharge requirements under specified constraints and operating costs. Feed-forward control is incorporated in the PI control configuration for preventing the influent loading disturbance affecting the process. No case studies of BSM1 model have been reported in the literature for the Indian wastewater. In this work, the dynamic simulation of an activated sludge process is performed using the data collected from the sewage treatment plant, located in India. The influent load data are collected during the dry weather period. The influent fractionation is carried out using the activated sludge model no.1 (ASM1). The results of the dynamic simulation indicate that FF-FB control of the activated sludge process is more effective than feedback control in meeting the constraints, especially effluent ammonia concentration which is considered as very important. From the comparison of performance evaluation criteria, it is observed that FF-FB control has achieved almost the same operating costs as with feedback control.

The hetero-/homogeneous combustion of methane-air mixtures in platinum-coated microreactors was investigated by means of two-dimensional CFD (computational fluid dynamics) simulations with detailed chemical reaction schemes, detailed species transport, and heat transfer mechanisms in the solid wall. Detailed homogeneous and heterogeneous chemical kinetic mechanisms are employed to describe the chemistry. The effects of the reactor size, inlet velocity and feed composition were elucidated. Operation strategies for controlling the heterogeneous and homogeneous chemistry in heterogeneous-homogeneous microreactors were developed. Simulations using these mechanisms suggested that homogeneous chemistry can be sustained for gaps well below the quenching distance because of enhanced catalyst-induced heating. This finding has very important ramifications for catalyst safety and lifetime, as well as can be used to produce chemicals, e. g. in oxidative coupling and oxidative dehydrogenation reactions. The proportion of heterogeneous and homogeneous contributions depends strongly upon the reactor operating conditions. Reactor size plays a vital role in the homogeneous chemistry contribution. Smaller reactors result in reduced homogeneous chemistry contribution. Pure heterogeneous chemistry can occur under certain proper conditions, such as heat loss/heat exchange rates, feed compositions, and flow rates. The competition or synergism between homogeneous and heterogeneous chemistry was delineated.

Malaysia is presently the world’s largest exporter of palm oil with total production of 19.22 million tonnes of crude palm oil (CPO) in 2013. Aside CPO, by-products such as empty fruit bunch (EFB), palm kernel shell (PKS), palm kernel oil (PKO), palm kernel cake (PKC) and pressed palm fibres (PPF) are produced from the palm oil mills. These biomasses can be used as potential feedstock for the production of biofuels, biogas and bioelectricity. One of the ways to fully harness the potentials of these biomasses is by employing the biorefinery concepts where all the products and by-products from oil palm are utilized for production of valuable bio-products. In this study, technological feasibility of biorefinery for the production of biodiesel, hydrogen, Fischer-Tropsch liquids (FTLs) integrated with combined heat and power (CHP) generation was investigated. Flowsheet was designed for each of the processes using Aspen HYSYS® v 8.0. Material balance was performed on a palm oil mill processing 250 tonnes per year of fresh fruit palm (FFP). Results from the material balance shows that 45.1 tonnes of refined bleached deodorized palm oil (RDBPO) and 52.4 tonnes of EFB were available for the production of biodiesel, hydrogen, FTLs and the CHP generation. The annual plant capacity of the biodiesel production is estimated to be 26,331.912 tonnes. The overall energy consumption of the whole process was estimated to be 36.0 GJ/h. This energy demand was met with power generated from the CHP which is 792 GJ/h leaving a surplus of 756 GJ/h that can be sold to the grid. The process modelling and simulation of the biorefinery process shows technological feasibility of producing valuable products from oil palm.

In this paper, Aspen Hysys v8.8 was used to simulate two strippers for sour water stripping process as the aim for removal of chemical impurities such as hydrogen sulfide, carbon dioxide and ammonia in wastewater. As a result of elimination of these impurities, the water can be reused. Comparison between single and two strippers and elevating the stripping efficiency was the objectives of the present study. The feed flow rate and compositions were specified according to the typical Chevron WWT process conditions. The simulation result shows that 100 % ammonia was stripped into the two stripper system but only 24 % stripped in the single stripper system. The result of H 2 O was almost same in both systems. The stripped water collected via the bottom of the Ammonia Stripper contains less than 10 ppm of hydrogen sulphide and less than 50 ppm of ammonia.