Supercritical Pipelines Research Articles

Achieving Supercritical Fluid CO2 Pressures Directly from Thermal Decomposition of Solid Sodium Bicarbonate

Compressing carbon dioxide (CO2) to supercritical pipeline pressures is one of the major costs of carbon capture and storage. Many innovative approaches to decreasing this cost have been suggested, in many cases relying on high temperature regeneration schemes utilizing high enthalpy solvents. Solid sorbent systems have not generally been examined for high pressure regeneration. We have now quantified through experimental and modelling studies that it is possible to obtain CO2 pressures of 150 bars or more by thermal decomposition of solid sodium bicarbonate (nahcolite, NaHCO3). In a cyclic operations with CO2 withdrawal, our model of the process predicts a swing capacity of 5% (wt.) when withdrawing CO2 at 20 bars, and 2% when withdrawing CO2 at 80 bars (supercritical fluid).Precipitation of solid sodium bicarbonate (“scaling”) has been observed previously when using sodium carbonate solutions in CO2 capture, and was considered an obstacle to the use of sodium carbonate as a capture solution due to potential mineral precipitation on the packing material. The ability to encapsulate the capture solvent overcomes the scaling problem and allows multiple benefits of the sodium carbonate capture solvent to realized [1]. In addition to high pressures of regeneration, these benefits include the low cost and benign nature of sodium carbonate, thermal stability with no thermal degradation, competitive carbon transfer mass when compared with amines, relatively low heat of solution of CO2 in the carbonate solvent, and potentially a reduced mass of water heated during regeneration.Using previous experimental data as well as our own measurements of CO2 pressures in equilibrium with carbonate solutions, we have developed a model of the phase behavior over a range of processing conditions of up to 210°C and saturation with respect to nahcolite. Using these data to parametrize a Pitzer electrolyte model, we predicted that in the absence of water, nahcolite reaches supercritical CO2 pressures over the solid at about 125°C. This encouraged us to pursue experimental determination with realistic amounts of water to allow for conversion of carbonate (CO32-) to bicarbonate (HCO3-) as loading with CO2 takes place. High CO2 pressures shift to higher temperature as the carbonate/water ratio decreases. However, encapsulated carbonates allow the system to operate at very high carbonate/water ratios such that a solid phase is present throughout the capture process. Each capsule contains mainly a solid carbonate phase with a small mass of saturated solution. Engineering of the capsule material may allow us to control both CO2 loading and water content independently to maximize CO2 carrying capacity and minimize water content, saving process energy by heating only minimal water during regeneration.

The Influence of Impurities on the Chocking Process of Supercritical Carbon Dioxide Pipeline

Transportation safety of supercritical CO2 pipeline is a key aspect of Carbon Capture and Storage(CCS). For reducing the high pressure in supercritical pipeline when accidental cases arise, man-made release will be applied using chocking process. The downstream parameters of chocking process can be predicted based on the adiabatic process assumption. The presence of SO2 as an impurity is helpful for increasing the downstream temperatures through the chocking device to prevent the frozen hazard, whereas the presence of N2 as an impurity indicates a lower downstream temperature. The higher initial temperature can prevent the dry ice formation at the outlet of vent pipe when the multistage chocking is applied. Keywords—CCS, carbon dioxide, pipeline transportation, impurity, chocking process

Safety Control on the Chocking Process of Supercritical Carbon Dioxide Pipeline

Transportation safety of supercritical CO2 pipeline is a key aspect of carbon capture and storage (CCS). For reducing the high pressure in supercritical pipeline when accidental cases arise, man-made release will be applied using chocking process. The downstream parameters of chocking process can be predicted based on the adiabatic process assumption. In the critical chocking process, the critical velocity at outlet is sonic. A chocking pipe can be designed for buffering between different chocking orifices according to the length of turbulence area produced by jetting momentum. For the effect of noise hazard produced by large jetting velocity, a muffler can be applied at the outlet of final stage orifice to atmosphere. For the influence of impurities on the chocking process of anthropogenic CO2 pipeline, the presence of SO2 as an impurity is helpful for increasing the downstream temperatures through the chocking device to prevent the frozen hazard, whereas the presence of N2 as an impurity indicates a lower downstream temperature. The higher initial temperature can prevent the dry ice formation at the outlet of vent pipe when the multistage chocking is applied.

Discussion of “ Drop Manholes in Supercritical Pipelines ” by George C. Christodoulou (January/February, 1991 Col. 117, No. 1)

Discussion of “ <i>Drop Manholes in Supercritical Pipelines</i> ” by George C. Christodoulou (January/February, 1991 Col. 117, No. 1)

Closure to “ Drop Manholes in Supercritical Pipelines ” by George C. Christodoulou (January/February, 1991 Col. 117, No. 1)

Closure to “ <i>Drop Manholes in Supercritical Pipelines</i> ” by George C. Christodoulou (January/February, 1991 Col. 117, No. 1)

Drop Manholes in Supercritical Pipelines

In urban drainage networks on steep terrain, drop manholes are often employed for energy dissipation and reduction of flow velocities. The hydraulic behavior of such circular manholes located between supercritical pipe segments is studied by means of laboratory experiments. It is found that the local head‐loss coefficient is governed solely by a dimensionless drop parameter, expressed in terms of the drop height and the inflow velocity. An analytical expression based on the experimental results is proposed for practical applications. The water level inside the manhole depends also on the angle between the inflow and outflow pipes, being higher when they are normal as compared to parallel. Optimum ranges of the drop parameter, in order to avoid impediment to the flow by formation of a hydraulic jump or surcharging of the pipe, may be determined and used in engineering practice.