T100 Micro Gas Turbine Converted to Full Humid Air Operation: Test Rig Evaluation

Abstract

Micro Gas Turbines (mGTs) are very cost effective in small-scale Combined Heat and Power (CHP) applications. By simultaneously producing electric and thermal power, a global CHP efficiency of 80 % can be reached. However the low electric efficiency of 30 % makes the mGT profitability strongly dependent on the heat demand. This makes the mGT less attractive for applications with a non-continuous heat demand like domestic applications. Turning the mGT into a micro Humid Air Turbine (mHAT) is a way to decouple the power production from the heat demand. This new approach allows the mGT to keep running with water injection and thus higher electric efficiency during periods with no or lower heat demand. Simulations of the mHAT predicted a substantial electric efficiency increase due to the introduction of water in the cycle. The mHAT concept with saturation tower was however never tested experimentally. In this paper, we present the results of our first experiments on a modified Turbec T100 mGT. As a proof of concept, the mGT has been equipped with a spray saturation tower to humidify the compressed air. The primary goal of this preliminary experiments was to evaluate the new test rig and identify its shortcomings. The secondary goal was to gain insight in the mHAT control, more precisely the start-up strategy. Two successful test runs of more than 1 hour with water injection at 60 kWe were performed, resulting in stable mGT operation at constant rotation speed and pressure ratio. Electric efficiency was only slightly increased from 24.3 % to 24.6 % and 24.9 % due to the limited amount of injected water. These changes are however in the range of the accuracy on the measurements. The major shortcomings of the test rig were compressor surge margin reduction and the limited energy transfer in the saturation tower. Surge margin was reduced due to a pressure loss over the humidification unit and piping network, resulting in possible compressor surge. Bleeding air to increase surge margin was the solution to prevent compressor surge, but it lowers the electric efficiency by approximately 4 % absolute. The limited energy transfer was a result of a low water injection temperature and mass flow rate. The low energy transfer causes the limited efficiency increase. The first experiments on the mHAT test rig indicated its shortcomings but also its potential. Stable mGT operation was obtained and electric efficiency remained stable. By increasing the amount of injected water, the electric efficiency can be increased.