FW Heater & Cooler

Heat Exchangers
Optimization of thermodynamic design

LP Feedwater Heaters, Didtrict Heaters and Duplex Heaters
HP Feadwater Heaters of tubesheet and header type
Water/water Coolers

Heat exchangers are especially handled by TPT.
In the tubesheet FWHs the tube bundle consists of bend tubes of U-form and the tubes are connected to the tubesheet. Th FWHs are arranged as vertical or horizontal heaters.

Tubes and tube bundle carrier:
( Patent: tube bundle carrier)(tube bundle carrier)

The tube material, tube diameter and water velocity are selected for the feed water heaters according to operational safety and economy. The tubes are expanded by rolling into the tube sheet. The bundle carrier is designed such that the tubes are protected against deformation and vibration and can freely expand. The support plates with the tube bundles can freely move in longitudinal and cross direction despite the unequal thermal expansion due to the hot and cold tube leg. The support plates show furthermore supports in the shape of wings in order for lateral guidance of the bundle carrier at the inner wall of the steam shell. The bundle carrier consists of support plates, side metal sheets, spacers and tie-rods which can be quickly assembled with little welding work and economically.


LP Feedwater Heater:
LP FWHs are designed as single zone with a condensing section or two zones with a condensing section and integral subcooler section. Drain coolers are employed because of heat consumption improvement in case of drain introduction into the lower heater through the level control valve.
Condensing heaters without subcooler section have a better heat consumption if the drain flows forward by using a drain pump. A drain pump is used usually for the drain of LP heaters No. 2 and 4.

HP Feedwater Heater:
( Patent AU 1404792: HP Feedwater Heater)

Tubesheet HP heaters are designed as two zones or three zones with condensing section, desuperheater and integral subcooler.
The use of a desuperheater reduces the terminal temperature difference (TTD) of the entire FWH. A negative TTD can be achieved by the use of a desuperheater. The limit of the theoretically possible desuperheating of steam is given by the condition of the still dry outer wall of the tube at the outlet of the desuperheater. The tube wall temperature must be over the local saturation temperature in all operation conditions.
The use of a separate cross-connected desuperheater improves the heat consumption and increases the feedwater temperature at the boiler inlet.
Drain coolers are employed because of heat consumption improvement in case of drain introduction into the lower heater through the control valve.

Header Type FWH:
These type of HP FWH has been developed to meet the increasingly severe operating conditions in large turbogenerator plants. These may include high heat rates, sudden load variations and frequent start-ups and shut-downs in case of peak-load power plants. The header type Heaters have lower maximum stresses during transient operating condition and therefore fewer potential failure mechanisms than tubesheet heaters. The tube bundle consists of multiple bend tubes and the tubes are connected to the thick-walled headers by means nipples.

For more information on Header Type FWH see:
"Header Type FW Heater as Retrofit for Cycling Units"
 Dr. M. Youssef, Power-Gen Europe 93: Mai 25-27, 1993 Paris 

Heat flow in:
Desuperheater section 3      Condensing section 2           Subcooler section 1

Q3=Mw x(hw3o -hw3i)    ,  Q2=Mw x(hw2o -hw2i) ,  Q1=Mw x (hw1o -hw1i)   [kW]
Q3=Mst x(hs3i -hst3o)    ,  Q2=Mst x(hs2i -hc2o)   ,  Q1=Mcon x(hc1i -hc1o)  [kW]

Heating area:
Ash =Qsh/(k3 . dTlog3) ,  Acon=Qcon/(k2 . dTlog2) ,  Asc =Qsc/(k1 . dTlog1) [m2]

Heat transfer coeffitient k:         k3, k2 and k1                 [kW/m2K]
Log. temperature difference:     dTlog3, dTlog2 and dTlog1     [K]


Duplex Heaters: 
( Patent: Duplex FW Heater)
( Duplex FW Heater)

Duplex feed water heaters for a steam power plant are arranged horizontal and normally are inserted into the condenser neck. A duplex heater consists of two heat exchanger modules (LP Heater 1/ LP Heater 2) in a common shell. The Modules are applied as pure condensing heat exchanger modules or with a condensing zone and with an integral drain cooler. The two heater spaces are defined through a partition wall in the shell and turbine extraction steam of different pressure and temperature is fed via inlet nozzles. The water to be heated flows from the water box through the U-tubes of the first heat exchanger module while the extraction steam with the pressure P1 condenses on the outer surface of the tubes. The water heated in heater 1, flows through the U-tubes of the second heat exchanger module and is further heated through the extraction steam with the pressure P2 (P2>P1) and flows again into the water box to the outlet nozzle.
The condensate is discharged at the bottom through two or more nozzles. The condensate flow of heater 2 is controlled through a control valve which controls the levels in the heat exchanger space 2. At a heat exchanger module with an integral drain cooler zone a flooded sectional bundle is chosen. The condensate of heater 1 flows via a siphon into the condenser.
Non condensing gases are sucked off over venting tubes which are positioned in the bundle lane at the zones of the lowest pressure.
The flows in the water box are achieved through the dividing the water box into three spaces by means of two internal shrouds or angular plates. The water box inlet nozzle is connected with the first shroud and the water outlet nozzle with the second shroud. Between both shrouds the feed water flows from heater 1 to heater 2.

The heat exchanger spaces are defined through a partition wall in the shell. The partition wall is carried out to a major part as a double-wall to provide insulation. Thereby the first wall which faces the heat exchanger space with the higher pressure is pressure bearing and the second wall which faces the heat exchanger space with the lower pressure serves as heat insulation and manufactured of thin sheet metal. For transmitting the force between the two walls thin metal sheets are provided. The space between the two walls is open through a number of holes at the bottom of the wall to the steam space with the lower pressure P1. The insulation provides a reduction in the heat loss flow and a power saving.
The load resulting from the pressure difference at the partition wall is transmitted via the support plates of heater 1 to the steam shell. The flexibility and the support of the partition wall avoid excessive stress at the connection place shell-partition wall due to heat expansion and over bending.



District Heaters:

District heaters (DHs) are built as condensing heat exchangers or with an integral drain cooler zone. DHs are designed for horizontal or vertical instalation. DHs are tubesheet type tubebundle heat exchangers with straight or U-tubes. The tubes are expanded into the tubesheet. By means of support plates the tube bundle are protected against harmful vibrations.
The steam flow is distributed over the entire bundle across an annular space between the shell and the tubebundle. The heating water flows through the heat exchanger tubes, while the extracted steam condenses on the outer surfaces of the tubes. The condensate accumulats in the heater hotwell. The incondensible gases are extracted over the bundle length in the zones of lowest pressure. A sufficient venting provides a good heat transfer coefficients for assuring a maximum utilization of the installed heat transfer surfaces. The tube bundle is usually protected against erosion due to high velociy at the steam inlet nozzle by an impingement plate.

Water/Water Coolers:( Patent: Condenser with integral water cooler)
( Condenser with integral water cooler) 
The water-water coolers are used for back cooling of water or condensate of cooling cycle and are arranged near the condenser. Water-water coolers (WWCs) are designed for horizontal instalation. WWCs are tubesheet type tubebundle heat exchangers with straight tubes and with one or two passes. The tubes are expanded into the tubesheet.
The cooling water inter the waterbox and flows through the heat exchanger tubes (tube side, cold side), while the water to be cooled, here called condensate (shell side, warm side) flows on the outer surfaces of the tubes. By means of support plates the condensate is deflected in counter cross flow to the cooling water and the tube bundle are protected against harmful vibrations.

Failures of HP Feedwater Heater Tubes:
The tube failure is one of the major causes of forced outages in fossil fired power plants. The causes of these failures are related to design problems, fabrication problems and operational problems. These basic problems can result in various types of damage to heater tubes. For example, design problems are related to high velocity in tubes, vibration, material selection, and tube to tube sheet joint. Problems related to fabrication include support plate drilling, welds, tube to tubesheet joint fabrication. Operational problems are related to cycling, startup, lay-up, low load operation, operation with excessive flow, flow out of leaking tubes, water chemistry etc. These problems result in a variety of damages to the feedwater heater tubes.

The top of problem are
- Steam impingement in desuperheat and condensing zone
- Tube vibration caused by high cross-velocity

Tube failures in a heater can be avoided by a well-planned inspection. Inspections during planned outages and inspections during forced outages.

Failures in desuperheater
Failures can occur in desuperheater and cause damages
- Damage caused by steam condensation at the desuperheater outlet
- High inlet steam velocity
- Tube vibration caused by high steam cross-velocity
- Damage at the desuperheater outlet due to interaction of condensate and steam flow

Failure in subcooler
- Excessive condensate velocities lead to local flashing of the condensate and subsequent collapse of the vapour bubbles, which is harmful when this agitation occurs close to tubes or other erosion-corrosion prone materials.
- Tube vibration caused by high condensate cross-velocity

Condencer System

Steam Condenser & Cooling Systems

The steam cycle power plants are equiped with cooled condensers where exhaust steam is condensed under vacuum. The operating condenser pressure is 0.03 to 0.4 bar and depends on the cooling system and medium temperature.

Three different steam condensers are used in two fundamentally different cooling systems:
1. Direct Cooling Systems:   a) One through cooling in surface condenser
  b) Dry cooling air condenser
2. Indirect Cooling Systems:   a) Wet cooling tower and surface condenser
  b) Dry cooling tower and direct contact condenser


1. Direct Cooling Systems

  a) Once Through Cooling in Surface Condenser: This open loop system has been achieved using water from a river, a stream or seawater. The cold wate is pumped through the condenser tubes and the warm water is discharged back to the water source. Surface condenser is explaned in wet cooling system.
  b) Direct Dry Cooling, Air Cooled Steam Condenser: Another form of condensing system is the air-cooled condenser. They are more environmentally acceptable forms of condensing steam. The process is similar to that of a radiator and fan. Exhaust steam from the low pressure section of a steam turbine runs through the condensing tubes. The heat transfered from the process steam to the cooling air via extended surfaces or tubes. The tubes are usually finned and ambient air is pushed through the fins with the help of a large fan. The steam condenses to water to be reused in the water-steam cycle.

The performance of dry cooling systems is primarily dependent on the ambient temperature of the dry air. Since the ambient dry air temperature is higher than the wet air temperature, dry cooling systems are less efficient than wet cooling tower design.
In dry cooling systems, the turbine exhaust is connected directly to the air cooled steam condenser (direct cooling system). The steam exhaust duct has a large diameter and is usually as short as possible to reduce pressure losses. An optimum fin tube geometry which give the highest heat transfer for the minimum amount of metal should be selected.

Advantages of dry cooling	Disadvantages of dry cooling
No water required	Duct pressure losses, less efficient
Can be located at fuel source	Large plot area required
No impact on environment	Generated more noise
Less permitting required	-

The condensation temperature in the condenser section is by 2-4 °K lower than the exhaust steam temperature, due to the steam pressure drop through the distributing duct and the heat exchanger tubes.

2. Indirect Cooling Systems:
  a) Indirect Wet Cooling System, Surface Condenser:
The need to reduce the amount of water requires a closed loop or wet cooling system. In a wet cooling system, water is circulated to condense the steam in the surface condenser. The warm water, instead of being rejected to the water source, is cooled in cooling tower using air as cooling medium. The wet cooling tower based on principle of evaporation.
The heated cooling water coming out of the surface condenser is cooled as it flows through a cooling tower, where air is forced through the tower by either natural draft or mechanical. The exhaust steam is condensed at the outside of the surface condenser tubes. Using cold water coming from the cooling tower.
Part of the cooling water is evaporated in the cooling tower, and a continuous source of fresh water (make-up water) is required to operate a wet cooling tower. The Make-up requirements for a cooling tower consists of the summation of evaporation loss, drift loss and blow-down.

Estimation of the evaporation loss: Meva = 0.0017 x Mcw x dTcool (dT in °K)
Drift is entrained water in the tower discharge vapors. Drift loss is a function of the drift-eliminator design. And a typical value is 0.005% of the cooling water flow rate.

Surface Condenser:
Water cooled condenser used in once through cooling system and in wet cooling system. The steam condenser is a major component of the steam cycle in steam power and combined cycle power plants. It is a necessary component of the steam cycle for two reasons:
- It converts the used steam back into feedwater for return to the boiler.
- It increases the cycle´s efficiency by allowing the cycle to operate with the largest possible Temperature and pressure difference between the boiler and the condenser.

Design principle: There are different condenser designs which are defined by suppliers. Condenser tubes are arranged as tube bundles in condenser shell with a single-pass or two-pass. The bundle shape and air cooler location are optimized by the supplier.
The design of single-pass condenser provides cooling water flow through straight tubes from the inlet waterbox on one end, to outlet waterbox on the other end. The design of two-pass condenser provides cooling water flow through straight tubes from the inlet waterbox, reversed in the return waterbox to the outlet watebox on the same end of Inlet waterbox.
In the condenser several thousand tubes are placed at low tube pitch in order to get acceptable dimensions. It is not favourable to increase friction losses in the steam flow, therefore the number of tube rows along the steam flow is limited. The separation between the water box areas and the steam condensing area is accomplished by two tubesheet to which the coolingwater tubes are attached. The cooling water tubes are supported within the condenser by the tube support plates.

The condenser tubes are made of brass or stainless steel to resist corrosion from either side. Nevertheless they may become internally fouled during operation by bacteria or algae in the cooling water or by mineral scaling, all of which inhibit heat transfer and reduce thermodynamic efficiency. Many plants include an automatic cleaning system that circulates sponge rubber balls through the tubes to scrub them clean without the need to take the system off-line.

 

The exhaust steam condensates on the outside of condenser tubes. The saturated liquid can continues to transfer heat to the cooling water. A few degrees subcooling prevents the condensate pump cavitation. The condensate subcooling or depression decreases the operation efficiency of plant because the subcooled condensate must be reheated. The condensat subcooling can be avoided by using a suitable bundle design. The condensate is collected in the hotwell which is arranged in the bottom area of the condenser where the condensate pump takes its suction.

Condensation heat Load:
    Q = Mcw x (hwout -hwin) = Mexh x (hsteam -hcond)     [kW]
Condensing area:             A = Q/(k x dTlog)     [m2]
Log. temperature difference: dTlog = (dTin -TTD)/(dTin/TTD)
dTin=(Tsteam-Twin)Overall heat transfer coeffitient k-value: the value of "k" depends on the heat transfer rate inside the tubes and condensation heat transfer rate outside, which is known worldwide in several norms.
The condenser is maintained at a vacuum using either vacuum pumps or air ejectors. Cooling of the steam is provided by Condenser Cooling Water pumped through the condenser by Circulating Water Pumps, which take a suction from water supplied from the ocean, sea, lake, river, or Cooling Tower (shown in cooling systems). The temperature and flow rate of the cooling water through the condenser controls the saturation pressure (vakuum) and the temperature of the condensate.
To prevent the condensate level from rising to the lower tubes of the condenser, a hotwell level control system is employed.
The performance of the condenser is dependent on the efficiency of its air cooler section. The condenser should be equipped with a highly effective air cooler section. The non-condensable gases should be collected and removed by venting system.

For combination of Surface Condenser with water cooler see:
Patent: Condenser with integral water cooler 
EP 1590603: Condenser with integral water cooler



b) Indirect Dry Cooling System (Heller System)
    Direct contact condenser and dry cooling tower
The turbine exhaust steam is air-cooled by means of intermediate heat transfer circuit with condensate quality water. The circuit water is circulated by pumps. Water films formed by the fill of this circuit condenses the exhaust steam in the direct contact condenser (spray condenser). A fraction of the warm circuit water, equal to the condensate stream, is pumped forward to the water-steam cycle by means of condensat pump or by using the circuit pump. The most of the warm circuit water is pumped via pipeline to a natural draft cooling tower where it cools down in water-to-air heat exchangers arranged vertically around the towers circumference.
The dry cooling system keeps approximately a constant temperature difference between exhaust steam and ambient air. This inlet temperature difference (ITD~30°K) is in reverse proportion to the dimension and price of the cooling system.

The Heller system offers a number of advantages:
Efficient condenser (TTD~0.3 K),
Condenser low-cost (four time less expensive than the surface condenser),
Simple and maintenance free
Lower condenser pressure in winter
No make-up is required, the system saves cooling water
The system is available with natural or mechanical draft tower
No fog is caused by the dry-cooling tower
Recovery water turbines are recommended, thus saving on pumping power

Due to reduction of the terminal temperature difference TTD and condenser pressure, the power of the turbine is increased compered with a surface condenser with a dry cooling tower. But the comparison is complete if the consequences on the overall economy of the cooling systems are investigated:
DC condenser with dry cooling tower and surface condenser with wet cooling tower. 

Nuclear Steam power plant

Nuclear Steam Power Plants

1. Pressurized Water Reactor (PWR)
Pressurized water reactors (PWRs) are nuclear power reactors that use ordinary water under high pressure as coolant and neutron moderator. The primary coolant loop is kept under high pressure to prevent the water from boiling. This puts strong requirements on the piping and pressure vessel and hence increases construction costs. PWRs are one of the most common types of reactors and are widely used all over the world. More than 230 of them are in use to generate electric power.
PWR has two coolant loops, so the water in the secondary loop is not contaminated by radioactive materials.
Ordinary water is used as primary coolant in a PWR and flows through the reactor at a temperature of roughly 315°C (600°F). The water remains liquid despite the high temperature due to the high pressure in the primary coolant loop (usually around 152 bar [2200 psig]). The primary coolant loop is used to heat water in a secondary circuit that becomes saturated steam (in most designs 62 bar [900 psi], 276°C [530°F]) for use in the steam turbine.

In a Secondary Cooling System (which include the Main Steam System and the Condensate-Feedwater Systems), cooler water is pumped from the Feedwater System and passes on the outside of those steam generator tubes, is heated and converted to steam. The steam then passes through the a Main Steam Line to the Turbine, which is connected to and turns the Generator. The steam from the Turbine condenses in a Condenser. The condensed water is then pumped by Condensate Pumps through Low Pressure Feedwater Heaters, then to the Feedwater Pumps, then to High Pressure Feedwater Heaters, then to the Steam Generators. The diagram above simplifies the process by showing the steam turbine, condenser, pumps, feedwater heaters, the steam generator, moisture separator and Reheater.

 

2. Boiling Water Reactor (BWR)The BWR typically allows bulk boiling of the water and is characterized by two-phase fluid flow (water and steam) in the upper part of the reactor core. The operating temperature of the reactor is approximately 300°C (570°F) producing steam at a pressure of about 70 bar (1000 psi). Current BWR reactors have electrical outputs of 570 to 1300 MWe.

The circulated water eventually is heated enough to convert to steam. Steam separators in the upper part of the reactor remove water from the steam. The steam then passes through the Main Steam Lines to the Turbine. The steam typically goes first to a smaller High Pressure (HP) Turbine, then passes to Moisture Separators, then to the 2 or 3 larger Low Pressure (LP) Turbines. There are 3 low pressure turbines, as is common for 1000 MWe plant. The turbines are connected to each other and to the Generator by a long shaft.

The steam, after passing through the turbines, then condenses in the Condenser, which is at a vacuum and is cooled by ocean, sea, lake, or river water. The condensed steam then is pumped to Low Pressure Feedwater Heaters. The water then passes to the Feedwater Pumps which in turn, pump the water to the reactor and start the cycle all over again.

Nuclear power plants generally cannot reheat process steam due to safety requirements for isolation from the reactor core. This limits their thermodynamic efficiency to the order of 34–37%.

Steam Power Plant

Steam Power Plants
In the steam cycle of a power plant the condensate from hotwel pumped to LP pressure, heated in LP feedwater heaters 1 to 4 and deaerated in the direct contact heater/deaerator 5. The feedwater pumped to high pressure, heated in HP heaters 6 and 7 before it enters the boiler where superheated steam is produced. The steam is superheated in the boiler to 540°C. The superheated steam is sent to the steam turbine where the steam expands to low pressure providing the energy to drive a generator. The exhaust steam from the low pressure turbine has to be condensated in the condenser in order to complete the steam cycle.
The exhaust steam enters condenser-tube bundles that have cooling water circulating through the tubes. The cooling water causes the steam to condense at a temperature of about 32–38°C and that creates an absolute pressure in the condenser of about 5–7 kPa, a vacuum of about 95 kPa relative to atmospheric pressure. The condenser creates the low pressure required to increase the efficiency of the turbines. The limiting factor is the temperature of the cooling water and that is limited by the prevailing average climatic conditions at the power plant's location.

Optimization of the feedwater heaters and the water-steam cycle improved the profitability and availability of the steam power plant.

Feedwater heating
The feedwater used in the steam boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinning steam turbine. The total feedwater consists of recirculated condensed steam, referred to as condensate, from the steam turbines plus purified makeup water. Because the metallic materials it contacts are subject to corrosion at high temperatures and pressures, the makeup water is highly purified before use. A system of water softeners and ion exchange demineralizers produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter. The makeup water in a 500 MWe plant amounts to perhaps 1.25 L/s to offset the small losses from steam leaks in the system.
The feedwater cycle begins with condensate water being pumped out of the condenser after travelling through the steam turbines. The condensate flow rate at full load in a 500 MWe plant is about 0.38 m³/s. The water flows through a series of six or seven intermediate feedwater heaters, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Typically, the condensate plus the makeup water then flows though a deaerator that removes dissolved air from the water, further purifying and reducing its corrosivity. The water may be dosed following this point with hydrazine, a chemical that removes the remaining oxygen in the water to below 5 parts per billion (ppb). It is also dosed with pH control agents such as ammonia or morpholine to keep the residual acidity low and thus non-corrosive.

 

Today the net thermal efficiency of the steam power plants lie between 0.42 and 0.47. The loss by the condensation of the exhaust steam is high and lie between 43% and 48% of the supplied heat flow.




Special Cycles for Steam Power Plants: 

Feedwater waters Circuit with Steam Desuperheater to the Deaerator:
Patent EP 0972911

LP Direct Contact Feedwater Heater Cycle:
Patent DE 19524216
Circuit for LP Feedwater Heaters:
Patent EP 1041251





Repowering of Existing Steam Power Plants
Repowering an existing steam power plant can be achieved by combining it, in whole or in part, with a gas turbine into a combined cycle plant. Repowering is ideal for plants in which the steam turbines, after many years of operation, still have considerable service- live expectancy, but the boilers are ready for replacement. The boilers are normally replaced or supplemented with gas turbines and HRSG. Some plants are repowered purely in order to benefit from the efficiency increase even though they are far from the end of their design life.
Repowering increases the output and efficiency of the power plant while improving plant reliability and decreasing plant emission.
The equipment to repowering will vary from case to case and depends on technical and economic criteria: Building and foundations, steam turbine and generator, condenser and cooling system.
The size relationship between the steam turbine and gas turbine is a main efficiency driver in a repowering application. It is important to have a good fit between the size of the gas turbine and the steam turbine.

There are three main options available when deciding to repower: 

1. Heat recovery combined cycle repowering 

The existing fired boiler is replaced with one (or two) efficient GT and one heat recovery steam generator (HRSG) by changing a part of the water/steam cycle. 


2. Hot wind box combined cycle repowering (HWBR) 

Steam power plants with reheat steam turbine can be repowered using the concept of "hot wind box". One (or more) gas turbine (GT) is installed and the high temperature GT exhaust gas flows first through the windbox of the present fired boiler to utilising the existing water/steam cycle and steam turbine (ST) and then through a waste-heat recovery heater used for most of the feedwater preheating. The rest of the preheating is done using the existing preheaters and steam turbine extractions. HWBR has a high degree of technical complexity. 


3. Heat recovery and fired combined cycle repowering (Hybrid PP) 

A new gas turbine and new HRSG are installed in parallel to the conventional boiler to provide a second source of HP live steam for the steam turbine. During normal load the existing fired boiler can operate the steam turbine. During high load the GT and HRSG of the combined cycle process can be utilized. This concept fits especially for large steam plants and offers more flexibility than other options due to the fired boiler and HRSG for meeting the load needs.
The exhaust heat at the cold end of the HRSG is used for preheating of partial feedwater. The existing steam extractions and feed heaters are used for preheating of the part of feedwater flow, allowing steam turbine extraction flows to be reduced and increasing steam turbine output.
Three operating modes are possible:
- Original mode without the gas turbine and HRSG in operation
- Hybrid mode, where the coventional cycle, gas turbine and HRSG are in operation
- Combined cycle mode, where the GT, HRSG and ST are in opration without the conventional boiler.
The highest overall efficiencies are obtained with pure combined cycle mode and the highest output with hybrid mode. 

Gas And Steam Power Plant

Gas and Steam Turbine Power Plants 
New Procedure for Increase of Efficiency & Powerdeveloped by TPT

Combined Cycles Power Plant CCPP

Today the CCPP is the most used power plants. CCPPs use a combination of two thermodynamic cycles: the gas turbine cycle (Brayton cycle) operating in a high-temperature and the steam turbine cycle (Rankine cycle) in a low-temperature range by using steam production in a heat recovery steam generator (HRSG). The combined cycle concept exploit the high-temperature potential of modern gas turbines and the low-temperature (cold end) of the steam cycle.

The combined cycle power plant offers high thermal efficiency, low emissions, low installed cost, flexibility in fuel selection and low operation and maintenance cost.
CCPPs are suitable for daily cycling operation due to short start-up times and for continuous base load operation. Part load efficiencies are also high due to the control of the gas turbine inlet mass flow using inlet adjustable vanes.

CCPP can be cooled by a cooling tower, a direct-cooling system or air-cooled condensers ensuring a wide range of applications. Where water is scarce, CCPP are advantageous because the cooling requirement is low due to the fact that the main coling requirement applies only to the steam process (33% of the supplied heat flow or 57% of total output).

The fuel flexibility of CCPP in limited to gases and some oils. The fuels that can be fired are those which are widely available in most parts of the world.

The main differences between combined cycle steam turbines and conventional steam turbines are:
- fewer or even no steam extractions for the feed water heating
- shorter start-up times
- lower live-steam pressures, 100 to 160 bar (160 to 300 bar by STPP)

Today the net thermal efficiency of the combined cycles power plants lie between 0.56 and 0.59. The losses by the exhaust gases and condensation of the exhaust steam are still relative high and lie between 40% and 43% of the supplied heat flow.



Research and the Development by Thermal PowerTec Ltd:

The research and the development of the water-steam cycle of combined power plants led to a new procedure for the reduction of exhaust steam losses and increase of thermal efficiency:

New Procedure 1:

   "A new combined cycles power plant with a single-supercritical-pressure HRSG"
   EP Ablication : April 2010
   Inventor :       Dr. Mustafa Youssef
   Applicant:       Thermal PowerTec Ltd, Zürich (CH)

The invention concerns a procedure to increase the thermal efficiency of gas and steam turbine power plants and especially of natural-gas combined-cycle. The gas turbine is combined with a single-supercritical-pressure HRSG. The live steam with a supercritical pressure expands by the HP steam turbine without a reheating to a wet steam state in the water steam zone below the water-steam boundary line. The steam wetness is removed by the moisture seperator and the LP evaporator.
A part of the separated condensate is led to the feed water. The saturated LP steam is reheated by the LP reheater and expands by the LP turbine to the condenser pressure.

Fig. 50a shows a single-supercritical-pressure used in HRSG.
Fig. 50b shows a temperature-entropy-diagram of the new process.
Fig. 50b shows a TQ-diagram for the energy transfer between gas and water-steam.

Compared to today's best combined cycle power plants with a triple-pressure HRSG and a steam reheating the new procedure allows an increase of the thermal efficiency of around 1%.
The thermal efficiency rises from for example 59% to over 60% and the output gain of the plant amounts to approximately 2%.

For the same electrical output of a CCPP this more environment friendly invention leads both to a reduction of the heat emissions of around 3% and to a reduction of the exhaust gas (CO2 and NOx) of around 2% into the environment.



Procedure 2:

"Procedure for increase the output and the thermal
efficiency of the combined cycles power plants"

   Publication Nr. EP 1 808 588, Date: 18.07.2007   Publication: pdf-file
   EP 1808588
   Inventor: Youssef Mustafa (CH)
   Applicant: Thermal PowerTec Ltd, Zürich (CH)

The research and the development of the gas turbine and steam turbine cycles led to a new procedure for the reduction of exhaust steam and exhaust gas losses below the 40% of the supplied heat flow.

The procedure concerns an improvement for combined cycles power plants (Fig. 27a. 27b & 27c). The gas in the gas turbine are expanded on a vacuum pressure, the gas are cooled by the HRSG, which are arranged in a vacuum container, and compressed by a gas compressor on the atmospheric pressure. The gas is further-cooled in the HRSG on the exhaust gas temperature.

In the gas turbine the supplied heat flow is increased by reducing the pressure of the 2. sequential combustion and the exhaust gas temperature is reduced by the gas expansion into the vacuum range. These make possible in the steam generator the use of a Single-pressure cycle with low exhaust gas temperature, in order to achieve minimum exhaust steam and exhaust gas losses. Thus the thermal efficiency of the combined cycles plant can be increased by more than 0.02 (i.e. hth net >0.60) and the power output by more than 18%.

In the gas turbine with vacuum expansion and sequential combustions the pressure of the LP combustion is reduced. The LP cooling air of the gas turbine taken from the air compressor by the corresbond pressure has a lower temperature and can be used, without cooling down. So only one gas turbine air cooler (HP air cooler) is necessary.


Construction of a CCPP with a vacuum gas turbine expansionin order to benefit from the present new procedure the use of the vacuum gas turbine expansion can be implemented without a large expenditure. All necessary elements (vacuum gas turbine stage, gas compressor and gas cooling in a vacuum container) are usual not complex parts in the power plant technology.

The following three options are possible:

Repowering of Existing CCPPs: CCPPs can repowered purely in order to benefit from the increase of efficiency and power output even though they are far from the end of their design life. Repowering an existing CCPP is possible and can be achieved by supplement of a vacuum gas turbine stage and a gas compressor and by changing a part of the HRSG.


Expected profits in a 300 MW CCPP:a) A power increase of 16% respectively 48 MW is expected. This can be evaluated with approx. 30 mil $. These will exceed the construction costs to a large extent.

b) The increase of the thermal efficiency of 2 per cent points results for a power increase of approx. 10 MW without fuel cost. This can be evaluated with approx. 1.8 mil $/year.



Gas Turbine Cooling The increasing of the hot gas temperature on the inlet of the gas turbine increases the efficiency of the gas turbine and thus of the CCPP. The problem of the gas turbine is particularly in the high temperature of the turbine blades. In order to bear the usual temperatures of 1000 to 1200°C, apart from the use of developed materials the turbine components are cooled additionally from the inside, by compressed and cooled cooling air.


Open Loop Air Cooling 
For this open cooling a part of the compressed air is removed on different pressure levels from the compressor and used for the cooling of combustion chamber and turbine blades. The extracted cooling air must be cooled down, before it used as cooling air in the turbine. After cooling of turbine components the cooling air is mixed in the turbine with the main gas flow.
Several concepts are available for matching the cooling requirements to the CCPP.
Open cooling concepts can be used for cooling the compressed cooling air:
- Water injection (quench cooler)
- Steam injection
- Water-Steam cooling in heat exchangers

For avoiding the loss of demineralised make-up water and the loss of evaporating heat energy in the exhaust gas, the use of water-steam-cycle for the air cooling in CCPP is the most economical solution.


GT-Air Cooler (Air/Water-Steam Heat Exchanger):
The air/water-steam cooler works as a steam generator. The cooling water is supplied from the feed water of the steam turbine cycle. In the gas turbine cooler the water is evaporated, superheated and return to the steam cycle.

The air/water-steam cooler has limitations of operation range. For a given bundle geometry the limitations depends on ambient temperature and inlet temperature/pressure of cooling water.

For more information on Air/Water-Steam GT-Cooler see:

"AIR COOLER FOR POWER STATION PLANT AND USE OF SUCH AN AIR COOLER"
 Inventor: YOUSSEF MUSTAFA (CH)
 Applicant: ALSTOM TECHNOLOGY LTD (CH)
  EP 1590603: GT Cooler

Closed-loop steam cooling
This steam cooling system permits the higher firing temperatures required for increased efficiency. Gas turbine cooling steam is supplied from the steam turbine cycle. The steam cools the gas turbine and return to the steam cycle. The closed loop steam cooling is in the development.
GE Power Systems developed the closed loop steam cooling (H System). The GE's H System permits the higher firing temperatures and designed with the capability to achieve 60% thermal efficiency.
The gas turbine cooling system is integrated with the steam cycle. The supply of cooling steam is from HP steam turbine exhaust. The steam is delivered to the gas turbine stationary parts through casing connections and to the rotor through a conventional gland connection. The cooling steam is returned to the steam cycle at the reheat line.

If the gas turbine steam cooling (H System) of GE Power Systems and the gas turbine vacuum expansion of TPT used in a combined cycle plant, then a net thermal efficiency of over 62% is expected.

GAS TURBIN POWER PLANT

Gas Turbine Power Plants
New Procedure for Increase of Efficiency & Power
Repowering of Existing GTPP developed bei TPT 

Existing Gas turbine power plant (GTPP)
GTPP in the whole consist of an air compressor, a gas turbine, gas turbine cooling system and generator (Fig. 028).
The gas turbine power plant offers low capital costs, quick installation, flexibility in fuel selection and low maintenance cost but low thermal efficiency and expensive demineralized cooling water.

Gas Turbine Air Cooling:
The problem of the gas turbine is particularly in the high temperature of the turbine blades. In order to bear the high temperatures, apart from the use of developed materials the turbine components are cooled additionally from the inside, by compressed and cooled cooling air.

Open cooling concept is used for cooling the compressed cooling air:
A part of the compressed air is removed on different pressure levels from the compressor and used for the cooling of combustion chamber and turbine blades. The extracted cooling air must be cooled down, before it used as cooling air in the turbine. After cooling of turbine components the cooling air is mixed in the turbine with the main gas flow.

Water Injection (quench cooler) is used in GTPP:
In gas turbine power plants usually the cooling air is cooled by water injection (Quench cooling) and be supplied as cooling air to the cooling system of the turbine. During such open air cooling with a water injection the previously demineralized water and its evaporation heat flow go lost with the turbine exhaust gases.

In particular in countries with dry regions it is to be found necessarily a new procedure with an effective cooling air cooling without a water consumption.

The research and the development of the gas turbine cycle led to a new procedure for the reduction of exhaust gas losses.




New Procedure for Gas Turbine Power Plants

"Procedure for increase the output and the thermal
efficiency of simple Gasturbine power plants"

     Publication Nr. EP 1 808 588, Date: 18.07.2007, Publication: pdf-file:
     Inventor: Y0ussef Mustafa (CH)
     Applicant: Thermal PowerTec Ltd, Zürich (CH)



1. Gas Turbine PP with Vacuum GT Expansion
The procedure concerns the increase of the power output and the thermal efficiency of gas turbine power plants. The gas in the turbine are expanded on a vacuum pressure, the gas are cooled by heat exchangers, which in a vacuum container are arranged, and compressed by a gas compressor on the atmospheric pressure. Furthermore the gas turbine cooling air is prepared without a water consumption. The cooling air is cooled by a water or a water-steam cycle, whereby the cooling circuit is connected with a heat exchanger in the cooling tower. The cooled air is led into the cooling system.

In the gas turbine the supplied heat flow is increased by reducing the pressure of the LP sequential combustion and the exhaust gas temperature is reduced by the gas expansion into the vacuum range. This lead to a low exhaust gas temperature, in order to achieve minimum exhaust gas losses. Thus the thermal efficiency (hth) of gas turbine plants can be increased by more than 0.06 (i.e. hth net >0.44) and the power output by more than 26%.

For a basis gas turbine plant with a net thermal efficiency of hth net = 0.384, the following Data are calculated:

Vacuum Pressure	Increased hth	hth net	Increased Output
0.60 [bar]	0.042	0.424	+22%
0.50 [bar]	0.052	0.434	+25%
0.40 [bar]	0.061	0.442	+27%
0.30 [bar]	0.065	0.447	+29%

In the gas turbine with vacuum expansion and sequential combustions the pressure of the LP combustion is reduced. The LP cooling air of the gas turbine taken from the air compressor by the corresbond pressure has a lower temperature and can be used, without cooling down. So only one gas turbine air cooler (HP air cooler) is necessary.


Construction of a GTPP with a vacuum gas turbine expansion
in order to benefit from the present new procedure the use of the vacuum gas turbine expansion can be implemented without a large expenditure. All necessary elements (vacuum gas turbine stage, gas compressor and gas cooling by means of water-steam cycles) are usual not complex parts in the power plant technology.

Expected profits in a 200 MW GTPP:
a) A power increase of 26% respectively 52 MW is expected. This can be evaluated with approx. 25 mil $. These will exceed the construction costs.

b) The increase of the thermal efficiency of 6 per cent points results for a power increase of approx. 26 MW without fuel cost. This can be evaluated with approx. 6 mil $/year.

c) With the new air cooling without a demineralized water consumption a saving of 1 mil $/year is to be expected.



2. Repowering of Existing GT Power Plants
Gas turbine plants can repowered purely in order to benefit from the increase of efficiency and power output even though they are far from the end of their design life. Repowering an existing GT power plant can be achieved by supplement of vacuum gas turbine stage and cooling system.
The equipment to repowering depends on technical and economic criteria:
Building and foundations, gas turbine and generator.

The following option is possible:
- Supplement of a separate vacuum gas turbine stage
- Arrangement of the gas turbine stage, a gas compressor and a Generator on a separate GT shaft
- Arrangement of a new cooling system with water/steam cycle and cooling tower.

Due to the cooling of exhaust gases and GT cooling air by the IP water-steam a steam flow rate is produced, which is separated from the water in the drum. A part this steam flow rate can be extracted and used for industrial purposes or for steam injection into the gas turbine (Fig. 029).

RADOAKTIVITAS

RADIOAKTIVITAS
RINGKASAN
Radioaktivitas adalah kemampuan inti atom yang tak-stabil untuk memancarkan radiasi
menjadi inti yang stabil. Materi yang mengandung inti tak-stabil yang memancarkan radiasi,
disebut zat radioaktif. Besarnya radioaktivitas suatu unsur radioaktif (radionuklida) ditentukan
oleh konstanta peluruhan (l), yang menyatakan laju peluruhan tiap detik, dan waktu paro
(t½). Kedua besaran tersebut bersifat khas untuk setiap radionuklida. Berdasarkan
sumbernya, radioaktivitas dibedakan atas radioaktivitas alam dan radioaktivitas buatan.
Radioaktivitas buatan banyak digunakan di berbagai bidang.
URAIAN
1. Definisi radioaktivitas
Radioaktivitas adalah kemampuan inti atom yang tak-stabil untuk memancarkan radiasi dan
berubah menjadi inti stabil. Proses perubahan ini disebut peluruhan dan inti atom yang takstabil
disebut radionuklida. Materi yang mengandung radionuklida disebut zat radioaktif.
Peluruhan ialah perubahan inti atom yang tak-stabil menjadi inti atom yang lain, atau
berubahnya suatu unsur radioaktif menjadi unsur yang lain.
Radioaktivitas ditemukan oleh H. Becquerel pada tahun 1896. Becquerel menamakan radiasi
dengan uranium. Dua tahun setelah itu, Marie Curie meneliti radiasi uranium dengan
menggunakan alat yang dibuat oleh Pierre Curie, yaitu pengukur listrik piezo (lempengan
kristal yang biasanya digunakan untuk pengukuran arus listrik lemah), dan Marie Curie
berhasil membuktikan bahwa kekuatan radiasi uranium sebanding dengan jumlah kadar
uranium yang dikandung dalam campuran senyawa uranium. Disamping itu, Marie Curie juga
menemukan bahwa peristiwa peluruhan tersebut tidak dipengaruhi oleh suhu atau tekanan,
dan radiasi uranium dipancarkan secara spontan dan terus menerus tanpa bisa dikendalikan.
Marie Curie juga meneliti campuran senyawa lain, dan menemukan bahwa campuran
senyawa thorium juga memancarkan radiasi yang sama dengan campuran senyawa uranium,
dan sifat pemancaran radiasi seperti ini diberi nama radioaktivitas.
Pada tahun 1898, ia menemukan unsur baru yang sifatnya mirip dengan bismut. Unsur baru
ini dinamakan polonium diambil dari nama negara asal Marie Curie, yaitu Polandia. Setelah
itu H. Becquerel dan Marie Curie melanjutkan penelitiannya dengan menganalisis pitch blend
(bijih uranium). Mereka berpendapat bahwa di dalam pitch blend terdapat unsur yang
radioaktivitasnya lebih kuat daripada uranium atau polonium. Pada tahun yang sama mereka
mengumumkan bahwa ada unsur radioaktif yang sifatnya mirip dengan barium. Unsur baru ini
dinamakan radium (Ra), yang artinya benda yang memancarkan radiasi. Detail dari
penemuan ini dapat dilihat pada pokok bahasan tentang Penemuan Radioaktivitas Alam.
2. Waktu Paro
Waktu paro (t½) adalah waktu yang diperlukan oleh suatu radionuklida untuk meluruh
sehingga jumlahnya tinggal setengahnya. Radiasi radionuklida mempunyai sifat yang khas
(unik) untuk masing-masing inti. Peristiwa pemancaran radiasi suatu radionuklida sulit untuk
ditentukan, tetapi untuk sekumpulan inti yang sama, kebolehjadian peluruhannya dapat
diperkirakan. Waktu paro bersifat khas terhadap setiap jenis inti.
Laju pancaran radiasi dalam satuan waktu disebut konstanta peluruhan (l) dan secara
matematik hubungan antara l dan t½ dinyatakan dengan
l = 0,693/ t½
3. Radioaktivitas alam dan buatan
Berdasarkan asalnya, radioaktivitas dikelompokkan menjadi radioaktivitas alam, dan
radioaktivitas buatan, yaitu hasil kegiatan yang dilakukan manusia. Dalam radioaktivitas alam,
ada yang berasal dari alam dan dari radiasi kosmik. Radioaktivitas buatan dipancarkan oleh
radioisotop yang sengaja dibuat manusia, dan berbagai jenis radionuklida dibuat sesuai
dengan penggunaannya.
4. Radioaktivitas alam
4.1 Radioaktivitas primordial
Pada litosfer, banyak terdapat inti radioaktif yang sudah ada bersamaan dengan terjadinya
bumi, yang tersebar secara luas yang disebut radionuklida alam. Radionuklida alam banyak
terkandung dalam berbagai macam materi dalam lingkungan, misalnya dalam air, tumbuhan,
kayu, bebatuan, dan bahan bangunan.
Radionuklida primordial dapat ditemukan juga di dalam tubuh mausia. Terutama radioisotop
yang terkandung dalam kalium alam. Uraian lengkap mengenai radioaktivitas alam dijelaskan
pada pokok bahasan "inti radioaktif alam (08-01-01-02)".
4.2 Radioaktivitas yang berasal dari radiasi kosmik
Pada saat radiasi kosmik masuk ke dalam atmosfer bumi, terjadi interaksi dengan inti atom
yang ada di udara menghasilkan berbagai macam radionuklida. Yang paling banyak
dihasilkan adalah H-3 dan C-14.
Kecepatan peluruhan dan kecepatan pembentukan radionuklida seimbang, sehingga secara
teoritis jumlahnya di alam adalah tetap. Berdasarkan fenomena tersebut, maka dengan
mengukur kelimpahan C-14 yang ada dalam suatu benda, dapat ditentukan umur dari benda
tersebut dan metode penentuan umur ini dinamakan penanggalan karbon (Carbon Dating).
5. Radioaktivitas Buatan
5.1. Radioaktivitas yang berhubungan dengan pembangkit listrik tenaga nuklir
Energi yang dihasilkan oleh proses peluruhan dapat digunakan sebagai pembangkit listrik
tenaga nuklir. Dalam instalasi pembangkit listrik tenaga nuklir, faktor keselamatan radiasi
menjadi prioritas yang utama, dan dengan berkembangnya teknologi pembangkit listrik
tenaga nuklir, maka tingkat keselamatan radiasinya pun semakin tinggi.
5.2. Radioaktivitas akibat percobaan senjata nuklir
Radioaktivitas yang berasal dari jatuhan radioaktif akibat percobaan senjata nuklir disebut fall
out. Tingkat radioaktivitas dari fall out yang paling tinggi terjadi pada tahun 1963 dan setelah
itu jumlahnya terus menurun. Hal itu disebabkan pada tahun 1962 Amerika dan Rusia
mengakhiri percobaan senjata nuklir di udara.
5.3. Radioaktivitas dalam kedokteran
Radioaktivitas yang berasal dari radioisotop dalam bidang kedokteran digunakan misalnya
untuk diagnosis, terapi, dan sterilisasi alat kedokteran. Uraian lengkap dari penggunaan
radioaktivitas di bidang kedokteran dapat dibaca pada pokok bahasan penggunaan radiasi
dalam bidang kedokteran.
5.4. Radioaktivitas dalam rekayasa teknologi
Penggunaan radiasi dalam bidang pengukuran (gauging), analisis struktur materi,
pengembangan bahan-bahan baru, dan sebagai sumber energi dibahas dalam pokok
bahasan penggunaan radiasi dalam rekayasa teknologi.
5.5. Radioaktivitas dalam bidang pertanian
Penggunaannya dalam bioteknologi, pembasmian serangga atau penyimpanan bahan
pangan, dan teknologi pelestarian lingkungan dibahas dalam pokok bahasan penggunaan
radiasi dalam produksi pertanian, kehutanan dan laut.

EFEK dan AKIBAT PENCEMARAN BENDA RADIOAKTIF

Efek dan Akibat dari Pencemaran Benda Radioaktif / Radio Aktif - Sinar Alpha, Beta dan Gamma Pembelahan Inti Atom - Ilmu Kimia

Pengertian atau arti definisi pencemaran radioaktif / radio aktif adalah suatu pencemaran lingkungan yang disebabkan oleh debu radioaktif akibat terjadinya ledakan reaktor-reaktor atom serta bom atom. Yang paling berbahaya dari pencemaran radio aktif seperti nuklir adalah radiasi sinar alpha, beta dan gamma yang sangat membahayakan makhluk hidup di sekitarnya. Selain itu partikel-partikel neutron yang dihasilkan juga berbahaya. Zat radioaktif pencemar lingkungan yang biasa ditemukan adalah 90SR penyebab kanker tulang dan 131J.

Apabila ada makhluk hidup yang terkena radiasi atom nuklir yang berbahaya biasanya akan terjadi mutasi gen karena terjadi perubahan struktur zat serta pola reaksi kimia yang merusak sel-sel tubuh makhluk hidup baik tumbuh-tumbuhan maupun hewan atau binatang.

Efek serta Akibat yang ditimbulkan oleh radiasi zat radioaktif pada umat manusia seperti berikut di bawah ini :

1. Pusing-pusing
2. Nafsu makan berkurang atau hilang
3. Terjadi diare
4. Badan panas atau demam
5. Berat badan turun
6. Kanker darah atau leukimia
7. Meningkatnya denyut jantung atau nadi
8. Daya tahan tubuh berkurang sehingga mudah terserang penyakit akibat sel darah putih yang jumlahnya berkurang

BAHAYA RADIOAKTIF

BAHAYA RADIOAKTIF

for everyone

Radioaktivitas pertama kali ditemukan pada tahun 1896 oleh ilmuwan PerancisHenri Becquerel ketika sedang bekerja dengan material fosforen. Material semacam ini akan berpendar di tempat gelap setelah sebelumnya mendapat paparan cahaya, dan dia berfikir pendaran yang dihasilkan tabung katodaoleh sinar-X mungkin berhubungan dengan fosforesensi. Karenanya ia membungkus sebuah pelat foto dengan kertas hitam dan menempatkan beragam material fosforen diatasnya. Kesemuanya tidak menunjukkan hasil sampai ketika ia menggunakan garam uranium. Terjadi bintik hitam pekat pada pelat foto ketika ia menggunakan garam uranium tesebut.

Tetapi kemudian menjadi jelas bahwa bintik hitam pada pelat bukan terjadi karena peristiwa fosforesensi, pada saat percobaan, material dijaga pada tempat yang gelap. Juga, garam uranium nonfosforen dan bahkan uranium metal dapat juga menimbulkan efek bintik hitam pada pelat.

Partikel Alfa tidak mampu menembus selembar kertas, partikel beta tidak mampu menembus pelat alumunium. Untuk menghentikan gamma diperlukan lapisan metal tebal, namun karena penyerapannya fungsi eksponensial akan ada sedikit bagian yang mungkin menembus pelat metal. Pada awalnya tampak bentuk radiasi yang baru ditemukan ini mirip dengan penemuan sinar-X. Akan tetapi, penelitian selanjutnya yang dilakukan oleh Becquerel, Marie Curie, Pierre Curie, Ernest Rutherford dan ilmuwan lainnya menemukan bahwa radiaktivitas jauh lebih rumit ketimbang sinar-X. Beragam jenis peluruhan bisa terjadi.

Sebagai contoh, ditemukan bahwa medan listrikatau medan magnet dapat memecah emisi radiasi menjadi tiga sinar. Demi memudahkan penamaan, sinar-sinar tersebut diberi nama sesuai denganalfabet yunani yakni alpha, beta, dan gamma, nama-nama tersebut masih bertahan hingga kini. Kemudian dari arah gaya elektromagnet, diketahui bahwa sinar alfa mengandung muatan positif, sinar beta bermuatan negatif, dan sinar gamma bermuatan netral. Dari

besarnya arah pantulan, juga diketahui bahwa partikel alfa jauh lebih berat ketimbang partikel beta. Dengan melewatkan sinar alfa melalui membran gelas tipis dan menjebaknya dalam sebuah tabung lampu neon membuat para peneliti dapat mempelajari spektrum emisi dari gas yang dihasilkan, dan membuktikan bahwa partikel alfa kenyataannya adalah sebuah inti atomhelium. Percobaan lainnya menunjukkan kemiripan antara radiasi beta dengan sinar katodaserta kemiripan radiasi gamma dengan sinar-X.

Para peneliti ini juga menemukan bahwa banyak unsur kimia lainnya yang mempunyai isotop radioaktif. Radioaktivitas juga memandu Marie Curie untuk mengisolasi radium dari barium; dua buah unsur yang memiliki kemiripan sehingga sulit untuk dibedakan.

Dewasa ini di beberapa negara maju pemanfaatan tenaga nuklir di berbagai bidang kehidupan masyarakat, seperti di bidang penelitian, pertanian, kesehatan, industri, dan energi sudah begitu pesat, maka sudah sewajarnya potensi tenaga nuklir yang cukup besar tersebut dikembangkan dan dimanfaatkan bagi sebesar-besar kemakmuran rakyat. Namun, di samping manfaatnya yang begitu besar tenaga nuklir juga mempunyai potensi bahaya radiasi terhadap pekerja, anggota masyarakat, dan lingkungan hidup apabila dalam pemanfaatan tenaga nuklir, ketentuan-ketentuan tentang keselamatan nuklir tidak diperhatikan dan tidak diawasi dengan sebaik-baiknya.

Pembinaan dan pengembangan kemampuan sumber daya manusia adalah syarat mutlak dalam rangka mendukung upaya pemanfaatan tenaga nuklir dan pengawasannya sehingga pemanfaatan tenaga nuklir benar-benar meningkatkan kesejahteraan rakyat dengan tingkat keselamatan yang tinggi. Pembinaan dan pengembangan ini dilakukan juga untuk meningkatkan disiplin dalam mengoperasikan instalasi nuklir dan menumbuhkembangkan budaya keselamatan. Zat radio aktif adalah setiap zat yang memancarkan radiasi pengion dengan aktivitas jenis lebih besar daripada 70 kBq/kg atau 2 nCi/g (tujuh puluh kilobecquerel per kilogram atau dua nanocurie per gram). Angka 70 kBq/kg (2 nCi/g) tersebut merupakan patokan dasar untuk suatu zat dapat disebut zat radioaktif pada umum-nya yang ditetapkan berdasarkan ketentuan dari Badan Tenaga Atom Internasional (International Atomic Energy Agency). Namun, masih terdapat beberapa zat yang walaupun mempunyai aktivitas jenis lebih rendah daripada batas itu dapat dianggap sebagai zat radioaktif karena tidak mungkin ditentukan batas yang sama bagi semua zat mengingat sifat masing-masing zat tersebut berbeda.

Pengertian atau arti definisi pencemaran zat radioaktif adalah suatu pencemaran lingkungan yang disebabkan oleh debu radioaktif akibat terjadinya ledakan reaktor-reaktor atom serta bom atom. Limbah radioaktif adalah zat radioaktif dan bahan serta peralatan yang telah terkena zat radioaktif atau menjadi radioaktif karena pengoperasian instalasi nuklir yang tidak dapat digunakan lagi.  yang paling berbahaya dari pencemaran radioaktif seperti nuklir adalah radiasi sinar alpha, beta dan gamma yang sangat membahayakan makhluk hidup di sekitarnya. Selain itu partikel-partikel neutron yang dihasilkan juga berbahaya. Zat radioaktif pencemar lingkungan yang biasa ditemukan adalah 90SR penyebab kanker tulang dan 131J.

Apabila ada makhluk hidup yang terkena radiasi atom nuklir yang berbahaya biasanya akan terjadi mutasi gen karena terjadi perubahan struktur zat serta pola reaksi kimia yang merusak sel-sel tubuh makhluk hidup baik tumbuh-tumbuhan maupun hewan atau binatang.

Efek serta Akibat yang ditimbulkan oleh radiasi zat radioaktif pada umat manusia seperti berikut di bawah ini : Pusing-pusing, Nafsu makan berkurang atau hilang, Terjadi diare, Badan panas atau demam, Berat badan turun, Kanker darah atau leukimia, Meningkatnya denyut jantung atau nadi.