A telescopic divergent chimney for power generation based on forced air movement: Principle and theoretical formulation

We present a new renewable energy technology concept for electricity generation based on an upward momentum created by a balanced forced air movement, which is initiated by an air blower, inside a telescopic divergent chimney constructed with adiabatic materials and equipped with a gas turbine. A theoretical model based on the principles of mass and energy conservation, and continuity was developed to investigate the forced air flow inside the system using a criterion defined as the difference between ambient pressure and static pressure at the outlet aloft of the chimney. The model results indicated that, as the air flow increasing to reach a threshold, there exists a steady state when the pressure difference equals to zero. At this state, a constant air flow velocity is attended such that the system becomes stable and the action of the blower is no longer required. In this condition, there is a non-linear relationship between the threshold velocity and the pressure difference with the geometry of the chimney, the installed load and ambient conditions are important dependent variables. With the estimated threshold velocity for chimneys from 15 to 150m, the steady-state distributions of velocity and energies (internal, potential, kinetic, enthalpy and extractable mechanical energy) at five cross-sections of the chimney were evaluated. The maximum velocity is found at the section with the minimum area, where maximum mechanical energy can be extracted. The maximum velocity can reach ∼45m/s in a 100-m high chimney. The extractable energy is found to have an exponential relationship with the chimney heights. The novelty of the concept is that when the air is forced to reach a threshold velocity in the system, the air can maintain a steady state without further supply of driving power.