Turing Machiene

"A Turing machine is a device that manipulates symbols on a strip of tape according to a table of rules. Despite its simplicity, a Turing machine can be adapted to simulate the logic of any computer algorithm, and is particularly useful in explaining the functions of a CPU inside a computer."                                                                                                          

In its simplest form, a Turing machine is composed of a "tape", a ribbon of paper of indefinite length. There is a "head" that can read the symbol, chose to write a new symbol in place, and then move left or right. The Turing machine is said to be in a certain "state". Finally, the program is a list of "transitions", that is a list that says, given a current state and a symbol currently under the head, what should be written on the tape, what state the machine should go, and whether the head should move left or right.
The tape is used to store data. In addition, it can also store a series of transitions (a small programs) and thus, the head can run "sub-programs". 

By analogy with modern computers, the tape is the memory and the head is the microprocessor. 
Although it is composed of pretty simple capabilities, Turing argued that this simple machine could performed any computation, that is, could realize anything that results from operations.

Schematic Diagram of Unit Auxilaries- Continuation of the previous article.

Principle of Operation of Thermal Station

In the some Thermal Stations, feed water is pumped with the aid of boiler filling pump into the drum; the water from the boiler drum flows downward through the down comers by gravity to the common headers which supply each of the tubes of which the furnace wall is made up of. The water is allowed to rise in the tubes above the burner level and the burners are lit off in an arranged order from the central control room.  The feed water gains heat energy up to the saturation temperature and the wet steam moves to the drum. As the drum is designed to be half filled with water, the upper part is for the wet steam.

A device called cyclone separator (with the aid of centrifugal system) separates the wet from dry steam before the dry steam leaves for the primary superheater.  The steam leaves the primary superheater for the secondary superheater, at this point the pressure is about 12.5Mpa at 541⁰C.  Just before the steam reaches the turbine blades, it losses about 1⁰C and steam at 12.5Mpa, 540⁰C impinges on the HP turbine blade. The heat energy is converted to mechanical energy on the HP turbine and the turbine spins.  The weak steam from the HP turbine exhaust is piped back to a heating system called reheater.  This is designed to raise the temperature back to 540⁰C but at full load (220MW) the pressure will be 3.3Mpa.

The steam from the Reheater is then sent to the intermediate pressure turbine.   (IPTBN) As the three stages of the turbine are linked via one shaft connected together with the generator a speed of 3000rpm is achieved at the generator end.

At the     LP turbine exhaust, the steam has lost almost all the energy and the LP exhaust temperature is as low as 45⁰C at the point of condensation! The makes it easier for condensation to take place in the condenser.  The steam condenses and settles beneath the condenser.  This is called “hot well”.  The pressure is far lower than atmospheric pressure and hence a large pump is required to pump the water because it has to overcome the negative pressure, take it to zero pressure (atmospheric pressure).  This is done with the aid of condensate extraction pump (CEP). The water is taken via steam jet Air Ejector, in order to remove all dissolved 0₂, to the condensate polishing plant.  The Booster pump increases the pressure as the water passes through LP HTR 1----> LPHTR 2-------->LP HTR3 and then to the Dearator.

The Dearator removes any remaining 0₂ in the feed water and serves as the HTR 4. The boiler feed pump (BFP) takes the feed water and increases the pressure to the boiler pressure to the boiler pressure.  The water is taken through HP HTR 5------>HP HTR 6------>he Economiser and then to the boiler Drum and the cycle begins again.

705tons/hr of dry steam (Dryness fraction of about 0.9) is required for 220MW.

Note: The following article describes one of the ways incorporated by thermal Power Plant.The following article is a piece from a reoport of Lagos Thermal Station by P. B. Osofisan.

Turbine Control Block Diagram

Turbine Control

The below figure gives a block diagram of power generation control.  On receiving turbine governor demand signals from the Automatic Boiler Control (ABC), the governor is put into operation, and main steam flow changes.  The flow rate of main steam fed to the turbine is converted into generated energy by the turbine generator.

Conventional governor control has been obtained by driving it directly with the turbine according to the control signals.  These signals are amplified by a proportional plus integral controller from the load dispatching values and the deviation signal of generator energy.  To further improve overall control in this case the main steam flow control has been added.  Also the cascaded control method that incorporates the above main steam flow control, has been included as a sub unit of generator energy control.Fig 4.1 gives a block diagram of power generation control.  On receiving turbine governor demand signals from the Automatic Boiler Control (ABC), the governor is put into operation, and main steam flow changes.  The flow rate of main steam fed to the turbine is converted into generated energy by the turbine generator.

Conventional governor control has been obtained by driving it directly with the turbine according to the control signals.  These signals are amplified by a proportional plus integral controller from the load dispatching values and the deviation signal of generator energy.  To further improve overall control in this case the main steam flow control has been added.  Also the cascaded control method that incorporates the above main steam flow control, has been included as a sub unit of generator energy control.

1.       Dispatching Value of Main Steam Flow Rate

The selection of main steam flow rate values in the turbine following mode is different from that of the coordinated control mode.

a)    Coordinated control mode (Not turbine following mode)

The dispatching values of the main steam flow rate are decided by adding advance signals based on the load dispatching values to corrected values of generated energy control.

b)    Turbine following mode

Dispatching values of the main steam flow rate are decided by correcting the program setting point based on the total fuel flow rate of boiler input using the deviation signals of the main steam pressure.

2.    Upper and Lower Limits Using Main Steam Pressure

Stable plant operation cannot be achieved if there is wide variation of main steam pressure, which exceeds the specified value.  Pressure should be immediately restored to its specified value.

Large variation in main steam pressure when operating under coordinated control is caused by a response delay of the boiler.  In order to lessen this variation, main steam pressure must be controlled by the turbine using a turbine governor which provides the most rapid effect on the main steam pressure.

3.   Turbine Governor Control

Main steam flow rate deviation signals are given to the proportional plus integral controller through a deviation limiting circuit for main steam pressure.  Governor opening signals, amplified by the proportional plus integral controller, will send turbine governor control signals after having passed through a manual/auto changing circuit.

Schematic Diagram of Steam Power Station

Components of Conventional Power Plant

The principal items of conventional or steam power plant are the boiler and the turbine. For these units a number of auxiliary units are also required.  A boiler uses coal, oil or gas as the fuel.  For this purpose, the fuel is stored in the coolant, a fuel handing plant is necessary to maintain a regular supply of fuel to the boiler.  This may again involved a number of smaller units.

Since the total weight of the fuel is not decomposed during combustion in the furnace while firing the boiler, thus a certain percentage of the fuel is collected as waste.  In case of coal fired boiler, almost 10-15% of the total weight of coal fired is collected in the form of ash.  Thus a station using 200,000 tonnes of coal/annum will produce in the average about 25,000 tonnes of ash. Such a huge quantity of ash from the furnace requires an ash handing equipment which will transfer ash from boiler furnace to ash storage.

Besides, air heaters may be used in plant to make use of the heat of flue gases which are always at elevated temperature.  Flue gases go to the atmosphere through the chimney, induced or forced draft fans may be used to create the necessary draft.

Steam from the boiler is supplied to the turbine where it expands thereby doing work.  Exhaust steam is passed to the condenser where it is condensed.  The condensate (i.e. H₂0) is pumped to the boiler by passing through high and low pressure heaters.

Condensers use H₂O for condensing steam. H₂O at the outlet of the condenser is relatively hot and may be cooled in the cooling tower and then recirculated.

Turbine is couple to the generator.  Output of the generator is supplied to consumer is relatively hot and may be cooled in the cooling tower and then recalculated.

Turbine is coupled to the generator.  Output of the generator is supplied to consumers through circuit breakers, transformers etc.