Moisture in refinery recycle gas with Panametrics
The catalytic reforming process converts low octane heavy naphta to high octane reformate for gasoline production. The process involves running dried naptha feedstock through a reactor containing a high value catalyst bed (typically platinum) at a high temperature and pressure for this conversion.
The recycled unconverted gas from the reactor is fed back into the reactor to increase the conversion rate. The moisture content in this process is typically maintained between 10-25 ppmv for optimal process efficiency.
The catalyst is activated by injecting Chlorides and a specific amount of moisture into the process. Too much moisture can cause formation of HCL which can lead to corrosion and of metal infrastructure and reduction of catalyst life while too little moisture can cause deactivation of the catalyst. The optimal amount of moisture is between 10-25 ppmv, this is controlled by continuous moisture measurement of the recycle gas to ensure feed dryers are working efficiently and the injection rate of moisture is correct.
Current technology utilized to monitor moisture levels in hydrogen recycle gas mixtures includes Quartz crystal microbalance (QCM) analyzers and Aluminum Oxide based probes. These methods have several drawbacks that can delay the moisture measurement, resulting in process excursions and off-specification product. QCM technology requires the sensor to be continually compared with a reference “zero” gas, which results in a non-continuous measurement. The self-verification requires the ability to generate a known moisture content using a desiccant, permeation tube and precise gas flow rates. As such, a QCM analyzer has a fairly complex internal sample handling system increasing the CAPEX and requiring significant maintenance, which increases OPEX as well. Aluminum oxide sensors can be impacted by coorosive gases typically found in this application during wet conditions such as start-up. These sensors also require annual calibration.
Panametrics Aurora analyzer uses tunable diode laser absorption spectroscopy (TDLAS) to accurately measure moisture in refinery recycle gas. It is certified for use in hazardous areas and its stainless steel construction and other inert wetted parts result in a hygrometer that doesn't drift and is immune to contaminants. An inbuilt sample conditioning system means there is no need of preconditioning, just connect the process gas to the Aurora and you are ready to measure. A backlit three-parameter LCD provides direct readout of measured parameters plus an indication of system status. The unit offers hard wired mA outputs and MODBUS digital communication.
Application specifications: Typical Moisture ranges: 0-1000 ppmv on startup, 0-50 ppmv normal operation
Laser technology had a number of advantages over other types of sensor technologies.
• Rapid speed of response, typically in seconds, to changes in process moisture, in both dry-to-wet and wet-to-dry conditions. • With no drift in calibration, tunable diode laser absorption spectroscopy (TDLAS) technology does not require recalibration, resulting in lower maintenance requirements and cost. • Non-contact measurement which eliminates the wear and tear on the optical sensing system from HCl or other process contaminants. • Integral sample system minimizes interference on the moisture measurement from other components in the process.
Learn more about our tunable diode laser absorption spectroscopy (TDLAS) hygrometers