Solar Energy Techonologies - Solar Steam Generating System for Cooking Application

Introduction

The solar steam generating system comprises of automatically tracked parabolic concentrators, steam header assemblies with receivers, steam pipelines, feed water piping, steel structures and civil works, instrumentation like pressure gauzes and temperature indicators, steam separators, steam traps etc. It is generally hooked up with conventional steam generating system already available with the user to make it reliable under all climatic conditions. Out of a total of 6 systems sanctioned by MNES till date, the world's largest system for cooking application has been installed at Tirumala Tirupathi Devasthanam (TTD), Tirumala, Andhra Pradesh whose details are given below:

The Solar Steam Cooking System at Tirupathi has been installed by M/S Gadhia Solar Energy Systems, Valsad under a demonstration scheme of MNES with around 50% support on solar part of the system. Balance of the cost has been borne by the TTD trust. The cost of the system is Rs. 109.00 lakhs which includes back up boiler, utensils and AMC for 5 years. The system has a capacity to prepare food for 15000 people/day and it employs automatic tracking solar dish concentrators, which convert water into high pressure steam. The steam thus generated is being used for cooking purposes in the kitchen of TTD.

The system has been designed to generate over 4000 kg. of steam/day at 180 degree c and 10 kg.cm2 which is sufficient to cook two meals for around 15,000 persons. It is of modular in nature and consists of 106 automatic tracked parabolic concentrators arranged in series and parallel combination; each of 9.2 sq. meter reflector area. Each unit of concentrators is connected to a central steam pipe line going to the kitchen. The system is made of indigenous components and the reflectors used are of acrylic mirrors having reflectivity over 75%. Its installation was completed during September, 2002 and was inaugurated by Hon'ble Chief Minister of Andhra Pradesh on 11th October, 2002. The system is functioning satisfactorily since then and is expected to save around 1,18,000 diesel per year. Other details of the system are as below :

Parabolic concentrators

Each parabolic concentrator of the system has a reflector frame fitted with reflectivity material, rotating support and a stand. The concentrators are installed in such a way that each two of them sharply focus sunlight to opposite sides of the receivers attached to a steam header. These concentrators are tracked automatically in east-west direction with the help of a central tracking arrangement. Seasonal adjustment is done on manual basis.

Receiver design

It is a shell type receiver made of MS, 35 cm in diameter and is connected to each two concentrators which focus the sunlight on both sides of this reciever. Various such receivers in a unit of concentrators are connected to a 12" dia header pipe which is half filled with demineralized water. The receivers and the header pipe are insulated to avoid any heat losses. Each receiver is integrated with two pipes of 1 ½" and ½" from inside which help in thermosiphonic flow of water from receiver to header and back. When the water gets heated in the receiver, it starts moving up in the header through one pipe and the cold water from header starts coming into the receiver. The cycle goes on and a high pressure steam is generated in the header after some time.

System functioning

Before the system is put into operation in the morning, all the header pipes are half filled with water using a high pressure reciprocating pump. All the concentrators are then arranged manually in the direction of the sun with the help of a central tracking arrangement. Once this is done all the concentrators then track the sun automatically with the help of a small DC motor run by PV panel. The time adjustment of tracking is made using a timer and a relay. The steam pressure starts building up in the header pipes immediately and is sufficient to deliver the steam in the kitchen in an hour or so. This steam can be drawn any time in the day even at the time of power failure as the feed water pump is not required to feed water and push the steam.

Payback period & Potential Users

The payback period of the system after availing financial support from MNES may vary from 3 to 5 years depending upon the size of the system. The technology could be successful at those places only where dedicated people exist to operate it and take care of the maintenance.These places could be religious ashrams, temples, gurudwaras, army canteens etc.

Main Application: Solar

Contact:

Ministry of Non-Conventonal Energy Sources,
Govt. of India
Block-14, CGO Complex, Lodi Road
New Delhi – 110 003
Tel: 91 11 2436 0707/ 2436 0404
Fax: 91 11 2436 1298

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