With the acceleration of industrialization and urbanization in China, wastewater treatment is increasing yearly. As a by-product of wastewater treatment, the gasification of sludge with coal in chemical looping process is a clean and efficient conversion technology. To explore the reaction behavior of cogasification of sludge and coal with iron-based oxygen carriers (OCs) for producing hydrogen-rich syngas, the experiment of cogasification using Fe2O3/Al2O3 as OC in a fluidized bed reactor was conducted. The result showed that the volume percentage of hydrogen (H2) and syngas yield is proportional to the amount of sludge added. The optimal operation conditions were: temperature at 900 °C, the mass ratio of OC to coal at 5.80 and mass ratio of sludge to coal at 0.2. Under this operating condition, the volume percentage of H2 and syngas yield in the flue gas was 75.6 vol% and 97.5 L·min-1·kg-1, respectively. Besides, the OC showed a stable reactivity in the sixth redox cycle with added sludge. However, the reactivity of OC significantly declined in the seventh and eighth redox cycles. It was recovered when the ash was separated. The decrease in the specific surface area of the OC caused by ash deposition is the main reason for the decline in its reactivity. The kinetic analysis showed that the random pore model describes the reaction mechanism of sludge/coal chemical looping gasification (CLG). The addition of sludge can reduce the activation energy of coal CLG reaction, accelerate the gasification reaction rate and increase the carbon conversion.
AbstractWe investigate the collective mode response of the iron-based superconductor Ba1−xKxFe2As2 using intense terahertz (THz) light. In the superconducting state a THz Kerr signal is observed and assigned to nonlinear THz coupling to superconducting degrees of freedom. The polarization dependence of the THz Kerr signal is remarkably sensitive to the coexistence of a nematic order. In the absence of nematic order the C4 symmetric polarization dependence of the THz Kerr signal is consistent with a coupling to the Higgs amplitude mode of the superconducting condensate. In the coexisting nematic and superconducting state the signal becomes purely nematic with a vanishing C4 symmetric component, signaling the emergence of a superconducting collective mode activated by nematicity.
Gelled acid systems based upon gelation of hydrochloric acid (HCl) are widely used in in both matrix acidizing and fracture acidizing treatments to prevent acidizing fluid leak-off into high permeable zones of a reservoir. The gelled up fluid system helps retard the acid reaction to allow deeper acid penetration for hydrocarbon productivity enhancement. The in-situ gelation is typically achieved by using crosslinked polymers with the acid. Conventional in-situ crosslinked gelled acid systems are made up of polyacrylamide gelling agent, iron based crosslinker and a breaker chemical in addition to other additives, with the acid as the base fluid. However, the polymer-based systems can lead to damaging the formation due to a variety of reasons including unbroken polymer residue. Additionally, the iron-based crosslinker systems can lead to scaling, precipitation and or sludge formation after the acid reacts with the formation, resulting in formation damage and lowering of hydrocarbon productivity.
In this paper we showcase a new nanoparticles based gelled acid system that overcomes the inherent challenges faced by conventional in-situ crosslinked gelled acid systems. The new system can work in 5 to 20 % HCl up to 300°F. The new system does not contain any polymer or iron based crosslinker that can potentially damage the formation. It comprises nanoparticles, a gelation activator, acidizing treatment additives along with HCl. The new in-situ gelled acid system has low viscosity at surface making it easy to pump. It gels up at elevated temperatures and pH of 1 to 4, which helps with diverting the tail end acid to tighter or damaged zones of the formation. We demonstrate that the viscosification and eventual gelation of the new system can be achieved as the acid reacts with a carbonate formation and the pH rises above 1. As the acid further reacts and continues to spend there by increasing the pH beyond 4, the gel demonstrates reduction of viscosity. This assists in a better cleanup post the acidizing treatment.
Various experimental techniques were used to showcase the development of the nanoparticle based acid diversion fluid. Static and dynamic gelation studies as a function of time, temperature and pH are reported. The gelation performance of the new system was evaluated at temperatures up to 300°F and discussed in the paper. Comparative performance of different types of gelation activators on the gelation profile of the nanoparticles is evaluated. It is also shown that the gelation and viscosity reduction is entirely a pH dependent phenomenon and does not require any additional breaker chemistry, and therefore provides more control over the system performance.
The novelty of the new gelled acid system is that it is based upon nanoparticles making it less prone to formation damage as compared to a crosslinked polymer based system.