Physical and Mechanical Properties of High Alumina Refractory Materials for shielding Applications of Steam Reformer Reactor

This research studied the physical properties of high alumina refractory materials, which are using as lining material in the primary and secondary reformer for Ammonia production in Kima project of Aswan City, Egypt .The study focused on the effect of materials balance variations of the mixture content, with different chemical recipes on The physical and mechanical properties which are affected by the in-service conditions of the primary and secondary reformer; these physical and mechanical properties are ; the bulk density, the thermal conductivity, permanent linear change (PLC), the cold crushing strength.


Introduction
Steam reforming of natural gas is the most common method of producing commercial bulk hydrogen at about 95% of the world production [1,2] of 500 billion m 3 in 1998. [3] Hydrogen is used in the industrial synthesis of ammonia and other chemicals. [4] At high temperatures (700 -1100 °C) and in the presence of a metalbased catalyst (nickel), steam reacts with methane to yield carbon monoxide and hydrogen ,according to the reaction;CH4 + H2O ⇌ CO + 3 H2.
Due to high temperature it is indispensable to use high durable refractory materials to resist and insulate such high temperature and keep the heat balance required to achieve the reaction. The refractory tiles supposed to be mounted in internal wall of the reformer as illustrated in the attached schematic design, Fig.1 [5] In this research i used high alumina refractory material, with a different chemical recipes of alumina, silica, iron oxide and titanium dioxide, CaO, Magnesia, Alkalis (Na2O+K2o),phosphorous Pentoxide [6] .the mixing and dry out of this mixtures was done in accordance to the technology provider of Reformer technology KBR [6] Table.1: The recipes percentage content by weight

Materials preparation
All minerals had been grinded and sieved to be less than 500 micron and then dried mixed for 10 minutes, to assure from homogeneity before wet mixing by water addition [16-21]

Wet mixing
In this step 10 kilograms of each sample ID after dray mixing were poured inside the mechanical vibrator mixer ( Fig.2.) for 10 minutes and then adding the total weight of water which representing 12% of the total weight of the sample, the pouring of the water shall be done into two half; one half after mixing 10 minutes and the other half shall be after 10 minutes,the wet mixing continue for 20 minutes [16][17][18][19][20][21]. there are controlling method to test the quality of mixing; called ball in hand test each sample is taken from the mixer and rounding it like a ball if the mixture was loose and not adhered then the mixer needs more water if the ball in hand was sticky and rounded it means that the water content is optimum, if the ball in hand was fluidized then the water is much more than required, Fig.3

Pouring in Cubic Molds
After adjustment and monitoring of the mixing process by ball in hand test, the mixed recipe of each sample from each category A,B,C,D were poured into wooden cubic molds with a dimensions 50X50X230 mm and dimensions 50X50X50mm to use it for the test required after curing and drying.The total number of samples to cover the required tests are 264 specimens.

Curing and Dry Out
At this stage all molded samples shall be dried and cured in accordance to the specifications of KBR design criteria, where it designed to the fitness for services [6].the regime of dry out and curing is to make ignition and heat up to 135 o C with a rate of 15 o C/hr, then hold 8 hours in temperature 135 o C, after that heating up to 300 o C at rate of 15 o C /hr. then holding temperature for 12hr ,then heating up the temperature to 480 o C at the rate 15 o C/hr and directly go forward to heat up the temperature to 950 o C at rate 50 o C/hr, then holding the temperature at 950 o C for 24hr,after that the temperature shall be descended to 200 o C at rate of 25 o C/hr.The curing and dry out regime is showed in Fig.4.

Sounding Test
The purpose of this test to sort the samples which have no any defect due to the casting and mixing or any defect regarding to the preparation to judge on the samples in according to variation of its material balance only. This test have been conducted by phased array technique by using apparatus of OMNISX-PA1664PR with 16 piezo electric elements. Test was done for all test samples and selected only the sounded samples and neglect all samples which have defects. The test have been repeated twice to increase the reliability as shown in Fig.5a,b where A scan showed no defect indications and also b scan but in C scan showed some textures indications regarding to sound noise but when repeated due to different calibration and neglecting the noise effect of the device showed completely sounded indications in Fig.5b.

Testing Required for Sample Evaluation
The test specimens of each category were tested and evaluated, where thermal conductivity test has been conducted by the device; DFX200 High speed Xenon-pulse delivery source and solid state PIN detector for unmatched sensitivity down to -150°C as shown in Fig.6.A., Also the bulk density was tested in accordance to ASTM C134 by device of XQK Ceramic refractory products apparent porosity bulk density as shown in Fig.6B., also cold crushing strength was tested in accordance to ASTM C133 by apparatus of PERCISION as shown in figure Fig.6C.., the permanent linear change also was tested in accordance to ASTM C113 by universal testing machine with furnace escalated temperature as shown in Fig.6.D

The Measurement of Bulk Density
The test samples in accordance to the recipes as illustrated in table 1 was tested by device of XQK Ceramic refractory to measure the bulk densities of test samples, the results showed (Fig.7)

Measuring of the Permanent Linear Change
The test samples were tested by apparatus of universal testing machine

Measuring of theThermal conductivity
The thermal conductivity was measured for test samples by apparatus DFX200 High speed Xenon, the results showed ( Fig.10)

Conclusions
 High alumina samples were tested and evaluated to be used as refractory materials for steam reformer reactor ,which it is main process for producing hydrogen required for ammonia production ,this articles provide the fabricator the ability to select the material which suitable for his application which required mechanical durability and low thermal conductivity, the data provided in this article make the fabricator has the wide range application to select material with low thermal conductivity and high mechanical properties .there was clear correlation between high bulk density and the high cold crushing strength where the sample Al01 showed the highest bulk density with value 3320 kgs/m3 and 3120 kgs/m3 at temperatures 105 o C,815 o C respectively and maximum cold crushing strength 80Mpa and 73Mpa at the same temperatures respectively where escalated alumina content contributed effectively to show high bulk density and high cold crushing strength .
 Regarding to the permanent linear change which it is important for the fabricator to receive materials with minimum linear change at highest temperatures, the sample Al12 (category C)showed minimum linear change at temperature up to 1820 o C with percentage up to 0.95%, where the balancing between alkalis and Cao with percentage up to 13.4% contributed effectively to receive such result.
 Regarding to the thermal conductivity also itis indispensable to get refractory materials with lowest value of thermal conductivity and also category C of sample Al10 showed lowest thermal conductivity at 0.81 w.m -1 .k -1 at highest temperature at 1315 o C.