Pilot Plant Calcine Research Articles

Modeling of the oxy-combustion calciner in the post-combustion calcium looping process

The calcium looping process is a fast-developing post-combustion CO2 capture technology in which combustion flue gases are treated in two interconnected fluidized beds. CO2 is absorbed from the flue gases with calcium oxide in the carbonator operating at 650°C. The resulting CaCO3 product is regenerated into CaO and CO2 in the calciner producing a pure stream of CO2. In order to produce a suitable gas stream for CO2 compression, oxy-combustion of a fuel, such as coal, is required to keep the temperature of the calciner within the optimal operation range of 880–920°C. Studies have shown that the calcium looping process CO2 capture efficiencies are between 70% and 97%. The calciner reactor is a critical component in the calcium looping process. The operation of the calciner determines the purity of gases entering the CO2 compression. The optimal design of the calciner will lower the expenses of the calcium looping process significantly. Achieving full calcination at the lowest possible temperature reduces the cost of oxygen and fuel consumption. In this work, a 1.7MW pilot plant calciner was studied with two modeling approaches: 3-D calciner model and 1-D process model. The 3-D model solves fundamental balance equations for a fluidized bed reactor operating under steady-state condition by applying the control volume method. In addition to the balance equations, semi-empirical models are used to describe chemical reactions, solid entrainment and heat transfer to reduce computation effort. The input values of the 3-D-model were adjusted based on the 1-D-model results, in order to model the behavior of the carbonator reactor realistically. Both models indicated that the calcination is very fast in oxy-fuel conditions when the appropriate temperature conditions are met. The 3-D model was used to study the sulfur capture mechanisms in the oxy-fired calciner. As expected, very high sulfur capture efficiency was achieved. After confirming that the 1-D model with simplified descriptions for the sorbent reactions produces similar results to the more detailed 3-D model, the 1-D model was used to simulate calcium looping process with different recirculation ratios to find an optimal area where the fuel consumption is low and the capture efficiency is sufficiently high. It was confirmed that a large fraction of the solids can be recirculated to both reactors to achieve savings in fuel and oxygen consumption before the capture efficiency is affected in the pilot unit. With low recirculation ratios the temperature difference between the reactors becomes too low for the cyclic carbonation and calcination. As a general observation, the small particle size creates high solid fluxes in the calcium looping process that should be taken into account in the design of the system.

Development of a Regenerable Strip Reagent for Treatment of Acidic, Radioactive Waste with Cobalt Dicarbollide‐based Solvent Extraction Processes

A regenerable methylamine carbonate (MAC)/diethylenetriamine pentaacetic acid (DTPA) strip solution has been developed, as a collaborative effort between the Khlopin Radium Institute (KRI) and the Idaho National Engineering and Environmental Laboratory (INEEL), for the stripping of actinides, lanthanides, Cs, and Sr from cobalt dicarbollide‐based solvent extraction processes. Methodology and experimental results of developing this strip reagent and a distillation method for regeneration of the resulting strip solution are presented. Additionally, countercurrent flowsheet testing of the Universal Solvent Extraction (UNEX) process, using 26 stages of 3.3 cm diameter centrifugal contactors, has been performed at the INEEL using dissolved pilot plant calcine and this regenerable strip solution. Results of stripping Cs, Sr, actinides, and lanthanides from the UNEX solvent with a MAC + DTPA strip solution that was freshly prepared and that has been regenerated are presented. Overall results of the flowsheet test are also presented.

Evaluation of ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) as a cesium selective sorbent for the removal of 137Cs from acidic nuclear waste solutions

Ammonium molybdophosphate (AMP) immobilized on polyacrylonitrile (PAN) is an engineered form of cesium selective sorbent material developed at the Czech Technical University in Prague. The selective cesium capacity of this inorganic ion exchange media was evaluated with simulated sodium bearing waste (SBW) and dissolved pilot plant calcine at the Idaho Nuclear Technology and Engineering Center (INTEC). Equilibrium isotherms were obtained at 23°C and 50°C with 48-h equilibrium contact times. The equilibrium isotherms were of the ‘favorable’ type and showed asymptotic maximum cesium loading of approximately 8.7% by weight of dry AMP. Dynamic column tests were performed with similar feeds using a 1.5-cm 3 bed in an up-flow configuration. Complete breakthrough curves were generated at feed rates up to 100 bed volumes (BV) per hour and sorbent capacities were determined to be approximately 32 g Cs/kg AMP-PAN (dry) at 100% breakthrough. Stop flow data were also obtained from the column tests. These stop flow data, in conjunction with column rate data, imply that cesium mass transfer is predominately particle diffusion limited at feed rates below 40 BV/h.

Solids flow and mixing model for a fluidized bed coating and calcination process

A model of the fluidized bed calcination process based on solids flow and mixing has been developed to calculate the change in the bed particle size distribution as a function of time and calciner operating conditions. The model is based on a mechanistic approach for determining the particle size distributions resulting from feed deposition, particle attrition, elutriation, seed addition and product removal. Comparison between the model results and data from a pilot plant calciner show good agreement. Because the model is based on mechanisms occurring in the fluidized bed calciner, it should be able to accurately scale up pilot plant results to predict operations in a full-scale calciner.