US 4,320,663 AGranted

Control system and method for controlling a solar energy plant

OwnerGiovanni Franciainventor

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Abstract

A solar energy plant comprises a solar energy boiler having pre-heating, evaporation, and superheating stages, and a control system for maintaining constant the temperature and the volume of the superheated steam at the boiler outlet upon variations in the incident solary energy. The flow of water entering the boiler is divided into a main flow, passing through the preheating, evaporation and superheating stages, and a secondary water flow. A first part of the secondary water flow is injected directly into the evaporation stage and a second part of the secondary water flow is injected directly into the superheating stage. The control system includes valve means for varying the rate of flow of the main water flow, and the first and second parts of the secondary water flow such as to maintain constant the temperature of the output superheated steam.

Claims26

Dependent claims

In a solar energy plant for the production of superheated steam of the type comprising a solar energy boiler having pre-heating, evaporation, and superheating stages through which a flow of water is arranged to successively pass between an inlet and an outlet of the boiler to transform the water from a liquid state into a superheated steam state, and a control system arranged to maintain constant the temperature and volume of superheated steam at the outlet of the boiler in the presence of variations of the solar energy absorbed by the boiler, the improvement wherein the said control system comprises:

means for dividing water entering through said boiler inlet into a main water flow to be passed successively through said pre-heating, evaporation, and super-heating stages, and a secondary water flow,
means for injecting a first part of the said secondary water flow into said evaporation stage and a second part of the secondary water flow into said superheating stage,
a main control loop for varying the flow rate of the main water flow as a function of the water temperature at a first point situated towards the downstream end of said preheating stage, the main control loop in operation acting to maintain the water temperature at said first point substantially equal to a desired value,
a first auxiliary control loop for varying the flow rate of the said first part of the secondary water flow as a function of the temperature T and the pressure p of the steam at a second point located in said superheating stage adjacent the upstream end thereof, said first auxiliary control loop in operation acting to maintain the value of the expression t-ap-b substantially equal to zero where a and b are two experimental constants dependent on the proportion of solar energy absorbed in the section of the boiler downstream of the said second point, and
second auxiliary control means for varying the flow rate of the said second part of the secondary water flow as a function of the temperature of the superheated steam at a third point situated adjacent the said outlet of the boiler, the second auxiliary control means in operation acting to maintain this superheated-steam temperature substantially constant.

2 more elements

A method of controlling a solar energy plant of the type comprising a solar energy boiler having preheating, evaporation, and superheating stages through which a flow of water is arranged to successively pass between an inlet and an outlet of the boiler to transform the water from a liquid state into a superheated steam state, the control method comprising the following operations:

dividing the flow of water entering the boiler into a main water flow which is passed successively through said pre-heating, evaporation and superheating stages of the boiler, and a secondary flow of water,
injecting a first part of said secondary water flow directly into said evaporation stage of the boiler and a second part of said secondary water flow directly into said superheating stage of the boiler,
varying the flow rate of the said main water flow as a function of the temperature of the water at a first point situated adjacent the downstream end of said preheating boiler stage such as to tend to maintain this temperature equal to a desired value,
varying the flow rate of said first part of the secondary water flow as a function of the temperature T and pressure p of the steam at a second point, situated adjacent the upstream end of said superheating boiler stage, such as to tend to maintain equal to zero the value of the expression T-ap-b, where a and b are two experimental constants dependent on the proportion of solar energy absorbed in the section of the boiler downstream of the said second point, and
varying the flow rate of the said second part of the secondary water flow as a function of the temperature of the superheated steam at a third point, situated adjacent said boiler outlet, such as to tend to maintain this temperature constant.

2 more elements

Dependencies are inferred from the claim text.