A New Type of Rotary Liquid Piston Pump for Multi-Phase CO2 Compression

Abstract

A novel rotary liquid piston multi-phase pump that transfers pressure energy from high pressure motive fluid stream to a low pressure process fluid stream within a high speed multi-ducted rotor is presented. The multiple ducts in the rotor act like cylinders of a rotating liquid piston pump with the liquid-to-liquid interface between the working fluid and the motive fluid acting like a piston. This novel pump has promise to solve challenges typically seen in multi-phase pumping and in trans-critical and supercritical CO2 compression systems, na m el y, risks due to phase change, two-phase compression inefficiencies, rotordynamic instabilities and sealing challenges etc. In this design the entrance and exit flow angles impart momentum to the rotor and the rotor achieves a self-sustained rotation without external power. The rotational speed dictates the volumetric efficiency, travel distance of the liquid piston within the ducts and the zero-mixing effectiveness of the design. This creates a very efficient pumping/compression system with just one moving part and three stationary parts, which can handle very high pressures and temperatures typical of supercritical CO2 turbomachines and also mitigates some of the rotordynamic stability challenges typically seen in MW-scale sCO2 turbomachinery designs. Ability of the pressure exchanger to dynamically maintain micro-scale gaps between rotor and stators through intelligent pressure balancing features relaxes the need to have complex dynamic seals. In this paper, use of this novel pump for multi-phase CO2 pumping application is explored through an advanced 3D multi-scale multi-phase flow model. The model captures the phase transport, compressibility, advection & diffusion of one phase into the other using a hybrid Eulerian-Lagrangian algorithm. Using these advanced models, performance curves are developed and results for key performance parameters including phase mixing, compressibility losses, effect of inlet gas volume fractions etc. are presented. A detailed transient evolution of two-phase fluid piston interface in the rotor ducts that captures acoustic wave propagation and reflection is presented. This new technology has promise to solve challenges typically seen in multi-phase pumping/ compression, transcritical and supercritical CO2 compression systems or in applications where the traditional pumps face steep challenges like phase change, erosive/ corrosive fluids, particle laden flows with high particle loading or flows with high gas volume fractions. This technology renders itself useful to several applications including supercritical CO2 turbomachines, waste pressure recovery, applications in oil & gas extraction and carbon sequestration etc.