The need for hydrogen in the refining industry has grown significantly as refinery feed-stocks have become heavier and sourer and fuel product specifications more stringent. The hydrogen produced in a refinery is used in hydroprocessing operations, and the resultant byproduct sour gas streams are routed to a sulphur recovery unit (SRU), which converts the H2S in these streams to elemental sulphur.
Both hydrogen production and sulphur recovery require very high reliability since any unplanned outage is extremely costly. Conventional materials of construction often do not deliver this desired level of reliability. Highly engineered ceramic systems have been developed with innovative designs and materials of construction to deliver improved reliability and performance for these processes.
The dominant process for manufacturing hydrogen is through steam methane reforming (SMR). Down-fired SMR furnaces utilize flue gas tunnels to collect flue gas and improve flow uniformity. However, nonuniform flue gas flow from conventional tongue-and-groove firebrick construction causes nonuniform catalyst-tube temperatures and accelerated tube aging. Also, SMR tunnels often fail due to multiple thermal cycles and poorly performing expansion joints. This leads to unexpected shutdowns and high turnaround costs. Failure scenarios for tunnels include greater expansion of the tunnel lids compared to the tunnel base and the overall tunnel attempting to expand more than the built-in allowance. This movement cracks the mortar, separates walls from lids and bases, and leads to failure.
New highly engineered refractory systems can significantly improve SMR tunnel reliability, flow uniformity and catalyst tube longevity. These systems incorporate customizable interlocking blocks that fit together in a mortar-free assembly and accurately accommodate thermal growth to offer excellent reliability. These can be used for new furnaces, revamps or just for the supply of tunnel lids. Field experience has demonstrated installation times of 10-15 percent that of conventional designs.
The reaction furnace (RF) in the SRU poses significant design challenges given its complex role in the conversion of H2S to sulphur and also for the destruction of contaminants including hydrocarbons, ammonia and BTEX (benzene, toluene, ethylbenzene and xylene). Even the best burners can't maintain complete mixing across the entire length of the RF, and internal structures such as checker walls or choke rings are often deployed to promote mixing. These structures are jointed with mortar and often fail due to thermal cycling and vibrations, leading to frequent, costly shutdowns and lost production. Damage to conventional checker walls can also cause inadequate temperatures for ammonia destruction, deposits of ammonium salts, plugging and expensive shutdowns.
Improved ceramic-based checker walls have been developed to address these problems. The walls consist of blocks designed to be stacked dry and that are mechanically engaged through a series of tabs and slots. No mortar is used between the blocks, with the interlocking assembly accommodating the thermally driven expansion and contraction. These features provide a much more stable wall that has now been demonstrated through several successful installations worldwide.
The most refined checkerwall design includes vectoring hoods that fit into the outlet of the blocks and significantly enhance mixing in the furnace while also better protecting the tubesheet and providing higher front-zone RF temperatures, energy savings and reduced emissions. These designs have also been deployed in sulphuric acid plants to reduce furnace size and NOx emissions. The walls are installed in less than half the time taken for conventional systems.
Highly engineered ceramic systems allow operating companies to achieve better reliability and installers to significantly decrease the total skilled labor hours required to complete field refractory work. Faster installation and longer time spans between replacements compared to traditional systems help address the growing manufacturing skills gap that often causes critical delays during planned and emergency turnarounds.
For more information, contact Uday Parekh at uparekh@blaschceramics. com or call (800) 550-5768.