Mariusz Markowski

Reconstruction of a heat exchanger network under industrial constraints - the case of a crude distillation unit

Abstract Heat exchanger network retrofit using a pinch based approach is presented. In this approach, the criterion of minimum sensitivity of heat exchanger to fouling effects is accounted for. The present paper introduces this criterion without explaining its details that are described in the literature. A summary is given of HEN reconstruction in a crude distillation unit processing 4.2 million ton crude oil per year. While the total heat quantity of hot streams is 110 MW, the heat recovery in the existing HEN is 60 MW. Using Pinch Analysis, the target value of heat recovery at ΔTmin=10 K was determined at 91 MW. Measurements were carried out on the existing HEN with the aim to determine the influence of fouling effects on the heat transfer in the exchangers. Taking local constraints including fouling into account, HEN reconstruction was proposed. The heat savings in the reconstructed HEN was estimated at 75 MW.

Calculation of heat exchanger networks for limiting fouling effects in the petrochemical industry

The paper presents a method for designing of heat exchanger networks (HENs), which reduces the effects of thermal fouling resistance. The method is based on pinch technology, extended by two transformations. These are based on the criterion of minimum sensitivity to the fouling effects by a single heat exchanger and the HEN. The proposed method has been applied in the petrochemical industry where the two heat recovery systems, designed by the method described here, have been working successfully for some years.

Integration study on a two-stage fermentation process for the production of biohydrogen

In order to make the hydrogen economy fully sustainable, renewable resources have to be employed for its production. Simulation models, developed with Aspen Plus to calculate mass and energy balances, will be used to integrate the process steps necessary to produce pure hydrogen from biomass in a 2-stage fermentation process. The main challenge is the reduction of water and heat demand connected to the low substrate concentration in the fermentation steps; the easiest solution is to partly recirculate outgoing process streams. Electrolyte equilibrium was considered during simulation of different recirculation options to evaluate important effects on the pH and on the system osmolality. The results show that certain recirculation options can reduce the heat and water demand significantly. (Less)

Heat integration of a fermentation-based hydrogen plant connected with sugar factory

The paper is concerned with heat integration of a conceptual hydrogen plant connected with a sugar factory. The sugar factory serves as a source of sucrose-containing thick juice for the hydrogen plant, where this feedstock is processed to hydrogen. Moreover, this connection gives an opportunity to utilize waste heat from the sugar factory. Hydrogen is produced by two-stage fermentation, that is, thermophilic fermentation followed by photofermentation. The gas mixture obtained in the two process stages is supplied to the gas separation system, composed of absorbing and stripping columns for circulating amine solution, to separate hydrogen from carbon dioxide. Using Pinch Technology and considering sugar factory with its CHP plant as an energy source, the hydrogen plant is heat-integrated to minimise the energy consumption. (Less)

Minimum Compressor Shaftwork in the Refrigeration System Thermally Coupled with a Rectification Column Network

There is considered the thermal separation of hydrocarbon mixtures using the rectification columns coupled, via a heat exchanger network, with a refrigeration circuit. Using the approach based on Pinch Technology, the minimum is sought of compressor shaftwork in the refrigeration system. The objective function is defined as the entropy increment resulting from the heat exchange in the heat exchanger network. The decision variables are the temperature levels of heat sinks and sources in the refrigeration cycle. An algorithm is proposed for determining the optimal values of the temperature levels of heat sources and sinks corresponding to the minimum of compressor shaftwork. The rectification columns are modeled using the ideal column approach. The numerical simulation is carried out by performing composite curves and selecting temperature levels in the refrigeration system so as to minimise the objective function. The test example is solved for a mixture of selected hydrocarbons (ethane, ethene, propene) to be separated in a sequence of rectification columns coupled with a refrigeration system. Assuming that structure of the rectification column network is known, process parameters are determined for minimum compressor shaftwork. Numerical results of the test example are presented.

A Neural Network Assisted On-Line Cleaning of Heat Exchanger Network

On-line cleaning of heat exchangers operating in a heat exchanger network (HEN) is aimed at preventing unnecessary losses of energy that can be recovered in HEN. If time behaviour of fouling in each heat exchanger can be estimated on the basis of past experience, then the optimal schedule of cleaning interventions can be determined by maximizing the objective function expressing the economic value of avoidable reduction in the energy recovery [1]. The crucial assumption for the presented paper is that on-line measurements of the mass flow and inlet and outlet temperature are available for each process stream. That made possible to evaluate fouling-induced reduction in the recovered energy flow using neural network model of HEN based on the measurements. The neural network (NN) model of HEN was applied in diagnostics of deposits influence on heat recovery in HEN by taking into account the time behaviour of fouling approximated by NN. The application of a neural network to the evaluation of changes in the energy flow recovered in a HEN has been tested using a simulated heat exchanger network as a reference. The simulation of HEN (implemented in MATLAB software) was based on a dynamic HEN model employing heat exchanger decomposition into interconnected cells whose overall dynamic behaviour is described by an array of lumped-parameter models. Computational aspects of the approach outlined above were studied on the example of a HEN featuring 26 process streams and 31 heat exchangers, operating in a crude distillation unit of 440 t/h processing capacity. A diagnostics of deposits influence on heat recovery in HEN makes it possible to attain a saving of about 5% of recoverable energy with the annual value of about 0,86 million USD.