Performance Evaluation of a Low Head Hydraulic Air Compressor: A Prospective Source of Renewable and Green Energy

Optimization Techniques for Hybrid Power Systems

Introduction

Hydraulic Air Compressor is a device that utilizes the energy of falling water, with entrained air bubbles, onto a downcomer pipe to compress the air within it. This concept to harness hydropower to compress air and its use dates back to the Iron Age. The basic principle behind it relates to concept of air entrainment in the water at the inlet to the sub-surface openings. The entrained air bubbles are carried downward, deeper and deeper, as a net effect of drag force of the water on the air bubbles and the buoyancy force of the bubbles along the downcomer pipe. At any depth below the free surface of water, the air bubbles experience pressure force from the surrounding water, which is proportional to the height of the water column above the bubbles. In this fashion it gets compressed to a pressure equal to the hydrostatic head at that depth. Normally an air separator is provided at the end of the downcomer pipe to collect the compressed air. In order to get accustomed, a schematic diagram of the principle of operation of a Hydraulic Air Compressor (HAC) is shown in Figure 1.

Figure 1.

Schematic diagram of operating principle of a Hydraulic Air Compressor

As can be seen from the principle, these types of compressors were extensively used in mining, lumbering and certain other applications in the United States, Canada and Europe during early 20^th century. Few large-scale HAC Plants were built in the beginning of the present century to supply mines with fresh air, and as a prime mover for the mining machinery. One of the biggest of those is the Ragged Chutes Plant on the Montreal River near the town of Cobalt, in northern Ontario’s silver mining country, was operational till late 1970s (Klein, 1977). However, in recent times, due to availability of other options, these compressors do not find a berth in present engineering practices. But, due to present crises of fossil fuels, and increasing need for using non-conventional renewable energy resources has again revived (Roy and Hazra,2014), (Hazra and Roy, 2021a,2021b).