Steam Boiler: Instrument

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Design Instrument Air System in Power Plant

Instrument air system in power plant is one of compressed air system. Instrument air system should be provided for control and instrument equipment. The equipment of instrument air system in power plant as follow:

Compressors with oil free screw type and has sufficient capacity.
After coolers and separators
Pre filters
Refrigeration type air dryers.
Air receivers
All piping, valves and supports in accordance with relevant sections of this specification.
All instrumentation including fitting, valves and installation material
Acoustic enclosure to house compressors and ancillary equipment
All electrical equipment and wiring associated with the above equipment, including local compressors control and selector panel suitable for compressors.

Isolating valve (locked shut) and check valve for connecting to an emergency air supply from the service air system to instrument air system should be provided in the power plant.

From the outlet of each receiver, a common header shall be equipped with the following connections but not limited to:

Isolating valve for Boiler
Isolating valve for Turbine
Isolating valve for CW pump house
Isolating valve for Water Pretreatment Plant
Isolating valve for Fuel Oil Storage area
Isolating valve for WaterTreatment Plant
Isolating valve for Chlorinationsystem
Isolating valve for Spare connections

The instrument air requirements for the turbine unit shall be taken from the appropriate connections provided on the air receiver common header.

Pipe work shall be sized and route to ensure minimum pressure losses throughout the system. All take off connections from horizontal headers shall be from the top of the main. Cooling water supply (if required) should be provided from closed cooling water system.

After Coolers and Separators

Each compressor shall he supplied with an after cooler and moisture separator complete with all necessary fittings, relief valves and automatic drainage facility.

Filters

In each of the three compressed air discharge mains positioned after the moisture separators shall be provided with a removable cartridge type filter. Each filter shall be capable of removing oil, water, dirt and other extraneous material from the compressed air.

Air Dryers

In each of the compressor discharge main shall be provided refrigerant type air dryer after air receivers. The air dryer should be supplied complete with refrigeration system, self- regulating hot refrigerant gas by-pass valve, chiller section, separator automatic condensate discharge trap and complete control system including moisture indicator, power-on light and safety switch. The air dryers shall be completed with by-pass piping and valves to facilitate servicing of each unit.

Air Receivers

The instrument air system can be provided as vertical air receivers. The receivers should be of all welded construction and shall conform to the requirements of ASME Section VIII "Pressure Vessel" Division I. The receivers shall be supplied complete with the outlet connections, manhole, drain connection, pressure gauges, relief valves and instrument connections.

Compressors

Each compressor shall deliver oil free air and shall be supplied with the following;

Water cooled intercooler with safety valve and moisture separator
Air intake filter and silencer to reduce noise
Unloading mechanism and piping
Relief valve
All control (local control panel), electrical and protection equipment to ensure safe and reliable operation of the plant.

Electronic Transmitter

Electronic transmitter has similar part with pneumatic transmitter, electronic transmitters also consists of two main parts, namely detector and sender. Figure 1 shows the structure of electronic transmitter.

Figure 1: Electronic Transmitter

The working principle of electronic transmitter is as follows:

- Trunk twist of detector is connected with the main counterweight of sender, so that the movement of trunk twist generates movement on the main counterweight.

- The movement of main counterweight change distance between two ferrites from detector to sender.

- Changed distance between two ferrites produces change in inductance of pick-up coil.

- Change in pick-up coil inductance produces change in oscillator output.

- Changes in the oscillator output produces change in electric current value that comes out of transmitter. Thus, changes in process variables are sensed by detector in the flavorings can produces changes in electric current value that comes out of sender. Thus position in which distance changes between two ferrites will be proportional to the change process variables which are sensed by the detector.

Transducers and Sensors

Transducers and sensors have close relationship each other. The definition of transducers and sensors is described as follow:

- Transducer

The transducer is a device that converts energy from one form to another. Transducers can be divided into two classes, namely input transducers and output transducers. Input transducers convert non-electrical energy, such as sound or light into electricity. Electrical output transducers working in the opposite order. The transducers convert electrical energy in the form of non-electric energy.

- Sensors

Sensors are devices used to detect and often serves to measure the magnitude of something. The sensor is a type of transducer used to convert variations in mechanical, magnetic, heat, light, and chemistry into voltage and electric current. Sensors are usually categorized by the measuring and has important role in modern manufacturing process. The sensors provide equivalent eye, hearing, nose, tongue to be microprocessor brain of industrial automation systems.

Thermocouple Transducer

The transducer is a component that works to convert physical parameters into electrical signals that can be accepted by the signal processing system. Several physical parameters are often known to be converted into electrical signals, among others: pressure, temperature, acceleration, shifting, speed, and so on. One of transducer type is thermocouple transducer.

Thermocouple transducer is the most widely used to measure temperature based on the conversion of temperature into electrical signal. Thermocouple transducer works based on the powerhouse at point of metal axis that is not same. This voltage is proportional to temperature of connection.

Figure 1: Thermocouple Transducer

Proportional Controller

Proportional controller is the control device that serves to strengthen error signal at desired level. In the proportional control, an output is obtained directly proportional to the proportional constant K. One example of the proportional control circuit is shown in Figure 1 below.

Figure 1: Proportional Controller

Integral Controller

Integral controller is a controller which serves to eliminate oscillations in the error signal. The output of this controller will generate output a ramp-shaped voltage (TIPA ramp) leading to an infinite value. In this case, the maximum is to the saturation value of op-amp near value of power supply voltage (VCC). One of integral controller circuit is shown in Figure 1 below.

Figure 1: Integral Controller

Proportional Integral Controller

Proportional Integral Controller is a control device that serves to eliminate the position error in steady state (steady position error). This controller is combination of proportional and integral control device that works in accordance with its corresponding respectively. Proportional controller performs lifting spontaneously while integral controller makes changes that increase gradually depending on the amount of time. Proportional Integral controller instrument type is shown in Figure 1 below.

Figure 1: Proportional Integral Controller

Scanning Electron Microscopy (SEM)

Scanning Electron Microscopy (SEM) is a method that can be used to observe the morphology of a material with magnification that far exceeds the ordinary optical microscope. Conditions to be met by sample material that would be characterized using scanning electron microscopy is should be conductive in order to be able to interact well with the primary electrons from electron gun in the scanning electron microscope. If sample material is not conductive, it should be coated with conductive material (e.g. gold) in order to form thin conductive layer on the surface of sample.

In the scanning electron microscope, electrons originating from the electron gun will strike surface of sample so that there is interaction between electrons originating from the electron gun (called primary electrons) with electrons present in the sample surface produces x-rays, secondary electrons, back Scattered electron and auger electron. Secondary electron is utilized and detected using detector to produce an image of characterized sample.

Spectrophotometer Diagram

Spectrophotometer Diagram can be described as follows:

Figure 1: Spectrophotometer Diagram

Description of spectrophotometer above:

1 = Radiation sources

2 = Monochromator

3 = Sample / cuvette

4 = Detector

5 = Amplifier and Recorder

Explanation:

Radiation sources

Some sources of radiation are often used in the spectrophotometer are: incandescent lamp with tungsten filament, hydrogen (deuterium) lamp, tungsten lamp, mercury lamp. Characteristics of energy that is emitted by each lamp varies whose function is to emit a radiation light that penetrates the sample that can later be read by recorder in which the source of the light radiation will pass through monochromator.

Monochromator

Sources of light is emitted from radiation source is focused onto entrance gap and then it is collected by gap or mirror and it is focused onto outer gap pass to the sample. The function of this monochromator is to obtain monochromatic radiation and then alter or transmit into polychromatic radiation.

Samples / cuvette

Most spectrophotometers involve solution so it requires a container / cuvette for placing the liquid / solution. Cuvette that is used should emit radiant energy in the spectral region. Reviewed from the used materials, there are 2 (two) types to make cuvette, namely: cuvette made from fused silica and cuvette made from glass. Cuvette from fused silica can be used for qualitative and quantitative analysis on measurement of 190-1100 nm region, and cuvette from glass can be used for in measurement of 380-1100 nm because of glass material can absorb light radiation.

Detector

After passing through sample, light radiation is received by the detector. Detector is one of important spectrophotometer parts so the selected detector must have high sensitivity to received radiation, has ability to respond radiation at wavelengths in unison. The function of detector in spectrophotometer is transforms received radiation signals into electronic signals. Received signal is then passed through an amplifier and finally accepted by the reader (recorder).

Amplifier and Recorder

Various tools can be used for reading generated signal by detector, including a calibrated meter to transmission or absorbance, digital readout systems, x-y recorder and computerized system.

Spectrophotometer

Spectrophotometer is an instrument consisting of spectro photometer and photometer. Spectrophotometer produces rays from spectrum with wavelength and photometer gauges for measure intensity of light which is transmitted or absorbed. So, the spectrophotometer is used to measure relatively energy if the energy is transmitted.

The spectrophotometer method is based on conversion of light polikromatis from the light source to be monochromatic light by a monochromator, and then it is passed through filter and will pass through the sample where some of light will be absorbed and some will be transmitted. This light will be detected by detector and it is amplified by the amplifier. The result will be recorded by recorder.

The relationship between radiation absorption with wavelength through the absorbing medium was first expressed by Bouguer, although sometimes it is ascribed to Lambert that his statement reads: "The power of radiation that is transmitted decreases exponentially if thick absorbing medium increases arithmetically. While Beer issued contradictory statements on Lambert's statement that the light which is used to be monochromatic, otherwise you will get two values of absorbance at two wavelengths."

If a system follows Beer's statement, a graph of absorbance against concentration will produce straight line, where the absorbance is directly proportional to concentration. Lambert and Beer's law indicates the relationship as follows:

Where:

a = constant absorption

b = distance optical

c = concentration

T = transmission

A = absorbance