Advanced Fouling Management through Use of HTRI SmartPM: Case Studies from Total Refinery CDU Preheat Trains

Abstract

Heat exchanger fouling is a persistent problem contributing to process economics, plant capacity, environmental concerns, and safety. Advances in research on hydrocarbon fouling have changed the impact of fouling in crude refinery operations, through the use of rigorous performance monitoring and process optimization methods, use of fouling predictive models, use of fouling mitigation technologies (e.g., use of tube inserts), etc. This work presents case studies from two TOTAL refinery preheat trains where the exchangers are subject to fouling. TOTAL has implemented a performance monitoring and predictive maintenance software (HTRI SmartPMTM) throughout their refineries to improve existing fouling management practice. The software performs advanced data reconciliation, including simulation of detailed exchanger operational data using HTRI shell-andtube heat exchanger calculation methods and inferring fouling resistance for individual shells for shells-in-series based on dynamic fouling behavior. Dynamic fouling models are used to assess the impact of fouling on the overall network performance. Several heat exchangers in the network have tube inserts (Turbotal and Spirelf inserts from Petroval), and their performances are monitored and predicted. The case studies demonstrate successful implementation of SmartPM software in TOTAL Normandy and Grandpuits refineries, enabling economically feasible, technically viable, and environmentally desirable decision-making for refinery operation. INTRODUCTION Crude refinery heat exchanger networks operate in a highly dynamic environment and strongly rely on practical fouling solutions. To date, a variety of practical fouling solutions are reported in literature [1, 2]; examples relevant to crude preheat train are listed in Table 1. Application of fouling mitigation options depends on a combination of decisions including the assessment of technical viability, economical feasibility, refinery philosophy, and operational strategy. Table 1: Examples of common fouling mitigation options (not exhaustive). Fouling mitigation options References Better heat exchanger design, retrofit, and network revamp [3–8] Alternative exchanger design (other than segmentally baffled exchangers) EMbaffles: [9, 10]; HELIXCHANGER: [11, 12]; Compabloc: [13–15] Improvements in operating strategies (e.g., flow split optimization, when and which units to clean) [16–22] Use of mechanical vibration devices for tube/tube bundle [23, 24] Use of tube inserts [25–27] Surface coatings [28] Better selection of crude [29] Use of anti-foulants [30–32] This manuscript describes case studies from two TOTAL refineries illustrating the strategic fouling management program via performance monitoring and predictive studies. TOTAL S.A. is a multinational integrated oil and gas company with worldwide presence in over 130 countries. TOTAL Refining and Chemicals (R&C) is a part of TOTAL S.A. that focuses on downstream processing. As part of TOTAL’s strategic industrial competitiveness, daily activities focus on operating assets as efficiently as possible on all the factors that can be controlled, including availability, energy efficiency, and costs. TOTAL initiated the implementation of SmartPM software as part of a project milestone and showcases TOTAL R&C’s strategy. SmartPM from HTRI is used for performance monitoring and predictive maintenance of heat exchanger networks. In this paper, SmartPM will be referred to as the simulator. The software is a digital twin technology, which mirrors operation of heat exchanger networks via connecting to the plant data historian. It can then predict the future performance of the heat exchangers and generate cleaning schedules to minimize energy use, maximize throughput, and lower CO2 emissions. SmartPM also allows users to look at possible revamp options for minimizing the thermal and hydraulic impact of fouling, such as altering heat exchanger designs or reconfiguring network structure. METHODOLOGY A systematic approach for fouling management was adopted (Figure 1) from best practices reported in literature (e.g., [4]). Heat exchanger and network model construction Heat exchanger models used detailed exchanger geometry from exchanger specification sheets and drawings. This geometry is used in the proprietary heat transfer and pressure drop correlations developed by HTRI. Several exchangers in the case study use two types of tube inserts (Turbotal and Spirelf). These are mechanical devices installed inside tubes to enhance heat transfer and to promote fouling mitigation. The tube insert geometries are also entered in the model. Turbotal inserts are rotating devices hooked on a fixed head set on the tubesheet on the inlet side. This system converts the energy of the fluid flow in the tubes into rotation. Spirelf inserts are vibrating devices secured on both tube ends by a fixing wire. This system converts the energy of the fluid flow in the tubes into vibration [33]. Piping and instrumentation diagrams (P&IDs) are used to construct the connection between the streams and the heat exchangers and also to identify the locations of isolation valves, monitoring data tags, and control structure. Process economics The economic details and hypothesis defined in this manuscript are for illustration and do not reflect the Normandy or Grandpuits refinery situations. The following parameters are used for the preheat train economics: cost of cleaning, 20,000 €; period when exchanger is offline for cleaning, 7 days; energy cost, 6.25 € /GJ; lost opportunity cost, 20 € /te; CO2 emission cost, 10 € /te. Data reconciliation Data reconciliation performs a heat and mass balance to generate missing process parameters from available temperature, flow, and pressure measurements. Fig 1. Flow chart of fouling management program. Fouling analysis A combination of different fouling deposits are observed throughout the preheat train [34, 35]. For exchangers located downstream of the desalter, even though some presence of salt/iron in the deposits may be observed [36, 37], the impact of fouling on the crude-side is proven to be dominated by chemical reaction fouling [36, 38, 39]. The case studies presented in this paper offer further confirmation. From Normandy plant experience, both the crude stream and heavy product streams are subject to fouling. A ‘dynamic fouling model’ relates the rate of fouling of the dominant fouling mechanism to the operating conditions of the exchanger. The use of the model requires pragmatic understanding of the fouling behavior throughout the heat exchanger network. Crude stream fouling (downstream of the desalter) is modeled via the asphaltene precipitation model: \uf028 \uf029 exp \uf061 \uf074 \uf0e6 \uf0f6 \uf03d \uf02d \uf0e7 \uf0f7 \uf0e8 \uf0f8 f dR E f dt h RT (1) Here, dRf /dt is the rate of change in thermal resistance, h is the film transfer coefficient, a is the fouling propensity factor which depends on the crude chemistry and the fouling surface, R is the gas constant, E is the activation energy of the conversion of maltenes to asphaltene cores [40], and \uf074 is the shear stress. Heavy hydrocarbon stream fouling is modeled via the particulate fouling model [41]: