Maintaining a controlled level of trace moisture content within hydrogen recycle gas is critical to the efficient operation of catalytic reformer processing of heavy naphtha feedstock; a crude oil distillate fraction with boiling point 100 to 160oC comprising mainly straight chain alkenes. The product from the reactions is reformate; higher octane complex hydrocarbon rings with high aromatic content. Both fixed-bed semi-regenerative reactor beds such as UOP Platforming and continuous catalyst regeneration reactors such as Axens Octanizing require moisture to be maintained with strict limits of 15 to 25 ppmV in order to achieve the desired level of acidity in the catalyst beds. High moisture concentrations increase the acidity and result in catalyst poisoning, while, conversely, low moisture levels reduce the acidic function and cause increased coking. Coke build-up requires increased reactor temperature to maintain the level of catalytic activity but also further accelerates the rate of coke formation. Only strict control of moisture concentration can achieve maximum catalyst bed lifetime.
This paper describes advances in moisture sensing techniques applying spectroscopic absorption methods to achieve improved real-time monitoring of recycle hydrogen gas. The benefits to process efficiency of applying this non-contact optical principle are discussed in comparison to the long established contact adsorption type moisture sensors that are still commonplace in refineries today, mostly applying quartz crystal microbalance measurement principle. Reduced cost of ownership and resource burden on maintenance staff are also considered.
This paper focuses on case studies which illustrate ‘Best Practices’ for improved moisture measurement through a number of evaluation trials at refineries.
Andy Benton joined Michell Instruments Limited in 1983, initially in R&D. Michell Instruments specialize in the measurement of moisture concentration, dew point, humidity and oxygen. Throughout his long career with Michell he has focused on devising innovative solutions to on-line process gas and liquid analysis applications. Most importantly as technical consultant to the natural gas industry, Mr Benton has advised best practice for moisture content and hydrocarbon dew-point measurement to producers, pipeline operators and large scale end-users within six continents.