OPTIMIZED PLANNING FOR DEVELOPMENT OF SMALL HYDRO POWER PROJECTS IN HIGH ALTITUDE AREA

Abstract

India is blessed with many rivers and mountains offering tremendous hydro potential of major, small, mini and micro hydropower. Contribution of small hydropower has grown substantially in the last ten years. Small hydropower (SHP) is one of the most common renewable, economic, non- consumptive, non-radioactive, non-polluting and environmentally benign sources of energy. The mountainous hilly regions suffer from the general impediments of difficult terrain, poor accessibility, poor transportation and poor communication facilities. A vast potential of small hydropower is available on high altitude areas. Development of the technology and equipment to exploit in this mountainous region at reasonable cost made the small hydro power plants not only to come into existence, but also made them popular. As per studies carried out Hydro Energy production is a major component of total energy production in most regions of India. Studies reveal that it is not always economical to operate a power plant without understanding the economic value of the water utilised for power generation. The design approach based only on the availability of water for power production is not always realistic during operation. The problems faced by the Small Hydro Projects in high altitude areas are sedimentation, landslides, transportation & construction of roads and Icing in water conveyance system. Due to this problem the SHP in India the Generations of Power is reduced or remain shut-down since water conductor system of the hydro project is all blocked by ice or silt since most of the structures of the hydro power plant do not have ice control structures or the desilting tank are manually operated. These difficulties have causes losses in generation and ultimately sizeable monetary losses. In this work studies will be carried only on icing problem in SHP civil structures i.e. trench weir, channels, desilting tank, forebay tank, trash rack and penstock. Icing problems at hydropower intake structures are usually caused by frazil ice. Intake weir or bar screens can be quickly and completely blocked when frazil ice forms in the flowing stream, upstream. Frazil ice is formed in turbulent, supercooled water. Supercooled water is at a temperature below its equilibrium freezing point. Supercooling takes place in rivers at locations where the water is turbulent, where the water surface is not covered by ice, and when the air temperature is less than 0°C (32°F) by a significant amount (usually an air temperature of —8°C (18°F) or lower is required). In this work, an attempt has been made to provide optimum solution for the factors affecting frazil ice in channels, forebay tank, desilting tank, trash rack and penstocks in small hydro scheme. If channels remain open for long periods during cold weather, large amounts of frazil ice can be formed, carried downstream by the flow velocity, and eventually deposited in a relatively slow velocity reach of the river to form a freeze up ice jam. Freeze up ice jams can block substantial portions of the river cross section. This blockage may raise upstream water levels enough to cause flooding, or may serve as the site of a breakup ice jam later in the winter season. Water intakes can experience significant problems with frazil ice if they are operated when the water is supercooled. Sufficient frazil can accumulate on the trash rack to effectively block it and completely stop the flow of water into the intake, often with severe consequences. Various mitigation techniques for protection and removal of ice have been carried out and some selected structural solutions were designed to check if optimization of cost can be done in between the compromise in the head loss and availability of water for water conveyance system for power generation and optimal selection was made. A case study is presented that describes the solution chosen to mitigate ice jamming problems. The methods employed include: a) Two proposals were compared and designed for protection of trench weir: 1. Using ice boom at the upstream of the intake. 2. Using heater. b) Three proposals were compared and designed for protection of power channel. 1) Proposed bed slope with steeper slope. 2) Power channel to be covered by a slab on which proper earth cover be provided. 3) Design the power channel with the margin of 600 mm higher depth for freezing. c) Two proposals were compared and designed for protection of forebay tank. 1. Covering the forebay tank at the top with slab. 2. Forebay with and extra depth of 600 mm for freezing. IV d) Two proposals were compared and designed for protection of desilting tank. 1. Covering the desilting tank at the top with slab. 2. Design the desilting tank with the margin of 600 mm higher depth for freezing. e) Two proposals have been compared and studied for protection of penstock: 1. Steel Penstock 2. GRP Penstock f) Two proposals were compared and designed for protection of trash rack. 1. Heater for Trash Rack 2. PVC Trash Rack. Cost of different alternatives were worked out and based on the cost and annual gain in revenue analysis; selection of the various alternatives of, Using heater in trench bar, Extra depth with 600 mm in power channel, forebay tank, desilting tank at the top with slab, using PVC in trash rack and GRP penstock was made. The cost of alternatives considered for extra depth of the channels, desilting tank, forebay tank with extra depth of 600 mm is optimum for freezing problems. The net installation cost and annual expenditure on extra depth of 600 mm can be recovered in six years as it increases the power availability of water in power plant throughout the year with head loss. The proposed alternatives for protection, removal of frazil ice and to ensure free flow of water from ice blockage can be used in Stakna SUP in order to run the project which usually remains shutdown during the winter season i.e. from December to March. Power will be available during this winter period and additional revenue will be generated. Review of these case studies will provide opportunity to connect ice blockage problems with successfully implemented solutions. .