(170b) Optimization of Mixed Smr Plant Using Advanced Modelling & Six Sigma Tools to Improve Energy Efficiency and Plant Performance: Case Study

Synthesis gas is the key feedstock for many industrial applications especially for ammonia, methanol, Oxo-alcohols etc. Most of the synthesis gas produced in the world is from natural gas using steam methane reforming (SMR). Mixed SMRs have carbon di-oxide added to the feed gas to produce synthesis gas with lower H2/CO ratio than that of conventional synthesis gas applications. As the gas reserves are depleting in the world, existing reforming plants are open to use natural gas from different sources. Different natural gas sources offer different compositions in the gas, which significantly affect the performance of the mixed steam methane reformers (SMR) in terms of reforming efficiency, energy consumption, H2/CO ratio in synthesis gas etc. Effect of feed gas disturbances in mixed SMRs is significant as these plants are operated at higher reforming temperature and lower steam to carbon ratios. In order to operate the reforming plant efficiently, optimally and smartly for all feed gas disturbances, optimization of the plant using advanced modelling & six sigma tools, precise pro-active control, continuous operations monitoring are necessary.

In this paper, an implemented optimization of mixed steam reformer in the oxo-alcohol production process case study is presented. An Aspen Plus model based study has been performed to optimize the mixed SMR plant operations for the existing feed gas composition. Then, coupled the model-based study with six sigma tools to develop the best operating conditions and zone for various scenarios. A number of contour diagrams have been developed for these scenarios using MINITAB, and response surface optimizer has been developed using response surface methodology. In this part, optimized the steam to carbon ratio, carbon dioxde to natural gas ratio, using surface response methodology using MINITAB, and the optimized conditions are translated into operator language and implemented in the systematic procedure. The implementation of the optimized conditions resulted in savings of energy 0.22 MMBTU/Ton of product and production increase of 2000 TPA.

Furthermore, a detailed dynamic model, as in the DCS of the plant, has been developed ASPEN DYNAMICS and analyzed the effects of the feed gas disturbances on the process. The analysis showed that H2/CO ratio in synthesis gas, reformer energy efficiency, methane slippage, and oxygen content in the stack gases would have serious repercussions and dynamic profiles have been developed for various feed gas compositions changes. In addition, it has been understood that a proactive advanced feed forward controls are necessary for reformer temperature, methane slippage, H2/CO ratio along with the existing feedback controls. Feed forward based control loops have been added on top of the existing controls based on the carbon number and calorific value of the feed gas. These upgradations enable the smooth operation of the plant during drastic feed gas composition changes. The added advanced process control would eliminate the situation of process upset and un-planned shutdowns, that result in improved equipment integrity and reliability.