Drying behavior of dense refractory castables. Part 2 – Drying agents and design of heating schedules

Heating rate effect on the moisture clog while drying refractory castables: A neutron tomography perspective

“…Figure 5B highlights how under slow heating conditions moisture accumulation initiates later, evolves slowly, most likely reducing the permeability at a correspondingly slower rate. These observations agree with TGA results, 23 and industrial observations 30 thus suggesting a direct relation between the heating rate and the likelihood of explosive spalling.…”

“…It is well known that faster temperature increases lead to a greater likelihood of explosive spalling as shown by TGA analysis. 3,10,23 However, the effect of the heating rate on the water distribution within the sample itself is still unknown as the available studies tackle the macroscopic response of the sample instead of its full-field response provided by imaging tests, such as the neutron tomography setup used by Moreira et al 17 Additionally, the most common technique applied for studying these effects, the TGA, generates a thermal gradient that is not representative of unidirectional heating attained when drying refractory linings in industrial applications, as schematically shown in Figure 1A. The unidirectional heating of the sample via the neutron tomography setup is shown in Figure 1B.…”

Microwave thermogravimetry as a tool to evaluate the drying of refractory castables – The effects of volumetric heating

“…This can actually be an interesting feature of this drying method as this fine-tuning capability of the temperature enables the possibility of detecting cooling regimes during the heating protocol. This cannot be reproduced by the conventional heating because even if the heater is completely shut down, the unidirectional nature of this method would lead to a heat front that would still be propagating through the material, as it can also be seen when imposing long plateaus on the drying curves [7].…”

“…To address this challenge, numerical models of this process were recently developed to help the design of the heating-up curves [5,6]. Another approach is based on the understanding and development of permeability enhancing additives that can speed-up the water withdrawn from the material, such as polymeric fibers [7]. The likelihood of in-situ observations of the drying process via neutron tomography has been also applied to further improve its understanding such as checking the moisture clog effect carried out by Moreira et al [8] As the temperature increase is the main driving force and control variable during the drying process [3], the search for alternative heating methods can also lead to important advances as suggested by the technical report on microwave drying by Taira et al [9], from Nippon Steel and by its numerical results presented by Gong et al [10].…”

Gas permeability of alumina–spinel refractory castables bonded with hydratable magnesium carboxylate

“…The aforementioned problems can be resolved by enhancing of gas permeability of these dense castables by forming permeable channels for water removal during the critical dehydration period and descending the internal vapor pressure. [1][2][3][4] The refractory castables are frequently bonded with calcium aluminate cement (CAC). And the permeability of modern castables could be enhanced to a certain extent by reducing CAC and water addition content.…”