2 Parts and How it Works plant: Boiler

PLTU Paiton, Jawa Timur

Steam Power (power plant) consists of several major systems, ie:

1. Turbine & Generator

2. Boiler (Steam Generator)

3. Coal Handling System

4. Ash Handling System

5. Flue Gas System

6. Balance of Plant

Turbine & generator can be regarded as the heart of the plant, because of the electrical energy is generated. Generator which rotates with constant speed, generating electrical energy supplied to the network interconnection and then distributed to consumers.

Steam turbine (steam turbine) which serves to turn a generator, consisting of HP (high-pressure) turbine, IP (intermediate-pressure) turbine and LP (low-pressure) turbine.
Turbine & generator has some supporting equipment, the lubricating oil system and the generator cooling system.

Boiler (steam generator) function to convert water into steam. Very high-pressure steam produced by boilers used to rotate the turbine. Boiler is divided into several sub-systems, namely:

- Boiler steel structure house
- Pressure parts
- Coal system
- Water system
- Boiler Cleaning System

 

Boiler (Steam Generator)
As the name implies, the boiler house structure is steel building steel frame structure, in which all equipment installed steam generator. This steel frame building height between 50 m (plant capacity of 65 MW) to 100 m (600 MW capacity power plant).
Pressure part system is a major part of the steam generator. These sections serve to convert water into high pressure steam (superheated steam) at temperatures between 500-600 degrees C.
Water supplied to the boiler, first came into the economizer inlet header, continue to be distributed to the economizer elements, reconvening in eco outlet header and then piped into the steam drum. Backpass economizer is located in the area (at the back of the boiler house), while the steam drum at the front of the roof area.
Named economizer as part of this serves to raise the temperature of incoming water boiler by utilizing exhaust gases from the combustion of coal in the furnace area (combustion chamber). By preheating the boiler economizer this efficiency can be improved.
Due to heating by convection in the furnace and due to gravity, water in the steam drum water circulation had dropped to the lower water wall headers via pipe downcomers. From the lower waterwall headers again experienced water circulation by heat, water rises toward the upper wall-tube headers via the tube water wall panels. Then from the upper waterwall header restored water to the steam drum through riser pipes.
So the result of coal burning hot water undergoes a continuous circulation. This circulation causes the water in a water wall panels & steam drum partially transformed into steam.
In a large-capacity power plant, boiler circulation is assisted by water circulating pump mounted on the bottom of the pipe downcomers. Faster circulation will cause the speed of the water changes into steam are also greater.
Inside there is a steam separator drum which serves to separate the steam from the water. The steam is separated, from the steam drum steam is channeled to the roof inlet header connected to the boiler roof panel. Boiler roof panel that carries the steam back into backpass panel.
of backpass panels, steam is channeled into the Low Temperature superheater (LTS) that is in backpass area, above the economizer elements. of LTS steam superheaters channeled into Intermediate Temperature (ITS). Next through the superheater pipe-desuperheater, steam superheater was taken to High Temperature (HTS) elements to undergo the final heating process becomes superheated steam.
ITS and HTS elements located inside the furnace (coal combustion chamber) the top. Some boiler manufacturers give different names to the LT, IT and HT superheater.
Of High Temperature superheater outlet headers, superheated steam with temperatures of 500-600 degrees C and very high pressure to the steam turbine channeled through the main steam pipe.
In the small-capacity power plant, the steam goes to the High Pressure Turbine, continues to Low Pressure Turbine and out into the condenser. While the large-capacity power plant, after turning the HP turbine steam is brought back to the boiler through the cold reheat piping.
Inside the boiler the steam to warm up again in Reheater elements. Reheater elements are usually located between the furnace area and backpass area.
After having re-heating, steam reheated to Intermediate Pressure Turbine channeled through pipes Hot reheat. After turning Intermediate and Low Pressure Turbine, a new steam out into the condenser.

0 How it Works Boiler

Heat energy generated in the boiler system has a value of pressure, temperature, and flow rates that determine the use of steam to be used. Based on all three systems recognize circumstances boiler pressure low-temperature (low pressure / LP), and pressure-high temperature (high pressure / HP), with the difference that the utilization of the steam out of boiler systems used in a process to heat your fluid and run a machine (commercial and industrial boilers), or generating electrical energy by converting heat energy into mechanical energy and then turn a generator to produce electrical energy (power boilers). However, there are also combining the two boiler systems, which use pressure-high temperature to generate electrical energy, then the remaining steam from the turbine with low pressure-temperature conditions can be utilized in industrial processes with the help of a heat recovery boiler.


The system consists of boiler feed water systems, steam systems, and fuel system. Water system provides water to the boiler automatically as needed steam. Various valves are provided for purposes of maintenance and repair of the system feed water, feed water treatment is required as a form of maintenance to prevent damage from the steam system. Steam system collects and controls the production of steam in the boiler. Steam is directed through a piping system to the user's point. The entire system, steam pressure is set using the faucets and monitored with a pressure monitor. The fuel system is all the equipment used to provide fuel to generate the necessary heat. Equipment required on the fuel system depends on the type of fuel used on the system.

2 Siklus PLTU Pembangkit Listrik Tenaga Uap

Sebuah pembangkit listrik jika dilihat dari bahan baku untuk memproduksinya, maka Pembangkit Listrik Tenaga Uap bisa dikatakan pembangkit yang berbahan baku Air. Kenapa tidak UAP? Uap disini hanya sebagai tenaga pemutar turbin, sementara untuk menghasilkan uap dalam jumlah tertentu diperlukan air. Menariknya didalam PLTU terdapat proses yang terus menerus berlangsung dan berulang-ulang. Prosesnya antara air menjadi uap kemudian uap kembali menjadi air dan seterusnya. Proses inilah yang dimaksud dengan Siklus PLTU.

Air yang digunakan dalam siklus PLTU ini disebut Air Demin (Demineralized), yakni air yang mempunyai kadar conductivity (kemampuan untuk menghantarkan listrik) sebesar 0.2 us (mikro siemen). Sebagai perbandingan air mineral yang kita minum sehari-hari mempunyai kadar conductivity sekitar 100 – 200 us. Untuk mendapatkan air demin ini, setiap unit PLTU biasanya dilengkapi dengan Desalination Plant dan Demineralization Plant yang berfungsi untuk memproduksi air demin ini.

Secara sederhana bagaimana siklus PLTU itu bisa dilihat ketika proses memasak air. Mula-mula air ditampung dalam tempat memasak dan kemudian diberi panas dari sumbu api yang menyala dibawahnya. Akibat pembakaran menimbulkan air terus mengalami kenaikan suhu sampai pada batas titik didihnya. Karena pembakaran terus berlanjut maka air yang dimasak melampaui titik didihnya sampai timbul uap panas. Uap ini lah yang digunakan untuk memutar turbin dan generator yang nantinya akan menghasilkan energi listrik.

Secara sederhana, siklus PLTU digambarkan sebagai berikut :

Siklus PLTU

1. Pertama-tama air demin ini berada disebuah tempat bernama Hotwell.
2. Dari Hotwell, air mengalir menuju Condensate Pump untuk kemudian dipompakan menuju LP Heater (Low Pressure Heater) yang pungsinya untuk menghangatkan tahap pertama. Lokasi hotwell dan condensate pump terletak di lantai paling dasar dari pembangkit atau biasa disebut Ground Floor. Selanjutnya air mengalir masuk ke Deaerator.
3. Di dearator air akan mengalami proses pelepasan ion-ion mineral yang masih tersisa di air dan tidak diperlukan seperti Oksigen dan lainnya. Bisa pula dikatakan deaerator memiliki pungsi untuk menghilangkan buble/balon yang biasa terdapat pada permukaan air. Agar proses pelepasan ini berlangsung sempurna, suhu air harus memenuhi suhu yang disyaratkan. Oleh karena itulah selama perjalanan menuju Dearator, air mengalamai beberapa proses pemanasan oleh peralatan yang disebut LP Heater. Letak dearator berada di lantai atas (tetapi bukan yang paling atas). Sebagai ilustrasi di PLTU Muara Karang unit 4, dearator terletak di lantai 5  dari 7 lantai yang ada.
4. Dari dearator, air turun kembali ke Ground Floor. Sesampainya di Ground Floor, air langsung dipompakan oleh Boiler Feed Pump/BFP (Pompa air pengisi) menuju Boiler atau tempat “memasak” air. Bisa dibayangkan Boiler ini seperti drum, tetapi drum berukuran raksasa. Air yang dipompakan ini adalah air yang bertekanan tinggi, karena itu syarat agar uap yang dihasilkan juga bertekanan tinggi. Karena itulah konstruksi PLTU membuat dearator berada di lantai atas dan BFP berada di lantai dasar. Karena dengan meluncurnya air dari ketinggian membuat air menjadi bertekanan tinggi.
5. Sebelum masuk ke Boiler untuk “direbus”, lagi-lagi air mengalami beberapa proses pemanasan di HP Heater (High Pressure Heater). Setelah itu barulah air masuk boiler yang letaknya berada dilantai atas.
6. Didalam Boiler inilah terjadi proses memasak air untuk menghasilkan uap. Proses ini memerlukan api yang pada umumnya menggunakan batubara sebagai bahan dasar pembakaran dengan dibantu oleh udara dari FD Fan (Force Draft Fan) dan pelumas yang berasal dari Fuel Oil tank.
7. Bahan bakar dipompakan kedalam boiler melalui Fuel oil Pump. Bahan bakar PLTU bermacam-macam. Ada yang menggunakan minyak, minyak dan gas atau istilahnya dual firing dan batubara.
8. Sedangkan udara diproduksi oleh Force Draft Fan (FD Fan). FD Fan mengambil udara luar untuk membantu proses pembakaran di boiler. Dalam perjalananya menuju boiler, udara tersebut dinaikkan suhunya oleh air heater (pemanas udara) agar proses pembakaran bisa terjadi di boiler.
9. Kembali ke siklus air. Setelah terjadi pembakaran, air mulai berubah wujud menjadi uap. Namun uap hasil pembakaran ini belum layak untuk memutar turbin, karena masih berupa uap jenuh atau uap yang masih mengandung kadar air. Kadar air ini berbahaya bagi turbin, karena dengan putaran hingga 3000 rpm, setitik air sanggup untuk membuat sudu-sudu turbin menjadi terkikis.
10. Untuk menghilangkan kadar air itu, uap jenuh tersebut di keringkan di super heater sehingga uap yang dihasilkan menjadi uap kering. Uap kering ini yang digunakan untuk memutar turbin.
11. Ketika Turbin berhasil berputar berputar maka secara otomastis generator akan berputar, karena antara turbin dan generator berada pada satu poros. Generator inilah yang menghasilkan energi listrik.
12. Pada generator terdapat medan magnet raksasa. Perputaran generator menghasilkan beda potensial pada magnet tersebut. Beda potensial inilah cikal bakal energi listrik.
13. Energi listrik itu dikirimkan ke trafo untuk dirubah tegangannya dan kemudian disalurkan melalui saluran transmisi PLN.
14. Uap kering yang digunakan untuk memutar turbin akan turun kembali ke lantai dasar. Uap tersebut mengalami proses kondensasi didalam kondensor sehingga pada akhirnya berubah wujud kembali menjadi air dan masuk kedalam hotwell.

Siklus PLTU ini adalah siklus tertutup (close cycle) yang idealnya tidak memerlukan lagi air jika memang kondisinya sudah mencukupi. Tetapi kenyataannya masih diperlukan banyak air penambah setiap hari. Hal ini mengindikasikan banyak sekali kebocoran di pipa-pipa saluran air maupun uap di dalam sebuah PLTU.

Untuk menjaga siklus tetap berjalan, maka untuk menutupi kekurangan air dalam siklus akibat kebocoran, hotwell selalu ditambah air sesuai kebutuhannya dari air yang berasal dari demineralized tank.

Berikut adalah gambaran siklus PLTU secara lengkap. (Klik pada gambar untuk memperjelas).

Siklus PLTU Lengkap

0 Inside Power Station

Generator Stator Cooling Water System

The Stator Cooling Water (SCW) system is used to provide a source of de-mineralize water to generator winding for direct cooling of stator winding and associated component.

Strainer are to remove debris in the 20 to 50 microns or large and filter for 3 micron.
De-ionizing sub system is required to maintain low conductivity 0.1 μs/cm. High conductivity can cause a flashover to ground in the stator winding.
Many de-ionizing system use the mixed bed type, employing both a strongly acidic cation resin and a strongly basic anion resin.

The content of copper and iron in the SCW is normally less than 20 ppb. High concentration of either could cause conductivity problem.

When no leaks are present in the system, hydrogen content is s minimum. High hydrogen content into SCW can cause gas locking and conductivity problem.

The dissolved oxygen content of the SCW is controlled to prevent corrosion of the hollow copper strand. Corrosion product can build up and block the cooling water flow. Oxygen at 200 to 300 μg/l produces at highest corrosion rate. The content pf oxygen in the SCW is normally maintained at less than 50 ppb in hydrogen saturated and low oxygen type system, and without limit for open vented or high oxygen type system.

High Oxygen refer to air-saturated water with dissolved oxygen present in the SCW in the range of grater than 2000 μg/l (ppb) at STP. The high oxygen system is based on supposition that the surface of pure copper forms a corrosion resistance and adherent cupric oxide layer (CuO) that becomes stable in the high oxygen environment.

Low oxygen refer SCW with a dissolved oxygen content less than 50 μg/l (ppb). The low oxygen system is based on the supposition that pure copper does not react with pure water in the absence of dissolved oxygen. The upper limit is set by the corrosion rate that the water cleansing system can handle. The lower limit is set to the level where copper will not deposit on any insulating surface in the water circuit such as hose. This is to avoid electrical tracking path to ground. It has better heat transfer properties at copper/water interface and a lower copper ion release rate.

pH value is manufacturer specific. Generally, there are two modes of operation, Neutral and Alkaline.
Neutral pH (7) with low oxygen content less than 50 μg/l is work best. Oxygen at 200 to 300 μg/l produces the highest corrosion rate, but high oxygen over than 2000 μg/l will also work.
Alkaline pH refer to high pH value around 8.5. Again, low oxygen work is best. However high oxygen will also work. This method requires an alkalizing subsystem to keep the pH at the proper level.

The SCW inlet temperature is maintain below 50C and outlet limit is 90C. The pressure set to 5 psi below hydrogen pressure to minimize the possibility water leakage into the generator. The flow velocities are design specific and are based on such thing as heat carrying capacity of water, cross sectional flow area in each bar and corrosion effect on the copper.

0 centrifugal pumps

The pump is a device or machine used to move liquids from one place to another through a medium piping by adding energy to the liquid is removed and continues over time.

The pump operates by the principle of making a difference in pressure between the entrance (suction) to the exit (discharge). In other words, the pump function transform mechanical power from a power source (driving) into kinetic energy (speed), where power is useful to drain the fluid and overcome the barriers that exist throughout the drainage.

Centrifugal pumps

One type of non-positive transfer pump is a centrifugal pump that works to change the principle of kinetic energy (velocity) of fluid into potential energy (dynamic) through an impeller which rotates in the casing.
In accordance with the data obtained, the reboiler pump debutanizer in Hidrokracking Unibon using centrifugal pump single - stage double suction.

Centrifugal Pump Classification

Centrifugal pumps can be classified, based on:

1. capacity:

     Low Capacity <20 m3 / h
     Medium capacity 20 -: - 60 m3 / h
     High-capacity> 60 m3 / h

2. Discharge Pressure:

     Low Pressure <5 Kg / cm2
     Medium pressure 5 -: - 50 Kg / cm2
     High pressure> 50 Kg / cm2

3. Number / composition of Impeller and Levels:

     Single stage: Consists of an impeller and a casing
     Multi stage: Consists of several impeller arranged in a single chassis series.
     Multi Impeller: Consists of several impeller arranged parallel in a single casing.
     Multi Impeller â € "Multi-stage: The combination of multi-impeller and multi stage.

4. Position Axis:

     vertical shaft
     horizontal shaft

5. Suction Number:

     Single Suction
     Double Suction

6. Impeller exit flow direction:

     radial flow
     axial flow
     mixed fllow

Main parts of Centrifugal Pumps

In general, major parts of the centrifugal pump can be seen like-the following picture:

                                                         Houses Centrifugal Pumps


A. Stuffing BoxStuffing Box serves to prevent leakage in the area where the shaft penetrates the pump casing.
B. PackingUsed to prevent and reduce the leakage of fluid from the pump casing through the shaft. Usually made of asbestos or Teflon.
C. Shaft (shaft)Shaft serves to continue the torque from the drive during operation and the locus of the impeller and other rotating parts.
D. Shaft sleeveShaft sleeve serves to protect the shaft from erosion, corrosion and wear of the stuffing box. In multi-stage pump can be as joint leakage, internal or interstage bearings and distance sleever.
E. VaneBlade of the impeller as a place of passage of fluid in the impeller.
F. CasingIs the outermost part of the pump that serves as a protective element that rotates, the seat of diffusor (guide vane), inlet and outlet nozzles as well as a place to give direction to convert the flow from the impeller and the fluid velocity energy into dynamic energy (single stage).
G. Eye of ImpellerThe side entrance on the direction of suction impeller.
H. ImpellerImpeller serves to convert the mechanical energy of the pump energy into velocity in the fluid being pumped continuously, so that the liquid on the suction side of continually going to fill the vacancy caused by the displacement of fluid that entered previously.
I. Wearing RingWearing the ring serves to minimize leakage of fluid passing through the front of the impeller and the back of the impeller, by minimizing the gap between the impeller casing.
J. BearingBeraing (bearing) function to withstand the burden of bearing and shaft to rotate, either in the form of radial loads and axial loads. Bearing also allows the shaft to rotate smoothly and remain in place, so that frictional losses become smaller.

 K. CasingIs the outermost part of the pump that serves as a protective element that rotates, the seat of diffusor (guide vane), inlet and outlet nozzles as well as a place to give direction to convert the flow from the impeller and the fluid velocity energy into dynamic energy (single stage).

0 Boiler feed water pump

A boiler feedwater pump is a specific type of pump used to pump feedwater into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler. These pumps are normally high pressure units that take suction from a condensate return system and can be of the centrifugal pump type or positive displacement type.

Construction and operation

Feedwater pumps range in size up to many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. Large industrial condensate pumps may also serve as the feedwater pump. In either case, to force the water into the boiler, the pump must generate sufficient pressure to overcome the steam pressure developed by the boiler. This is usually accomplished through the use of a centrifugal pump.
Feedwater pumps sometimes run intermittently and are controlled by a float switch^{[citation needed]} or other similar level-sensing device energizing the pump when it detects a lowered liquid level in the boiler. The pump then runs until the level of liquid in the boiler is substantially increased. Some pumps contain a two-stage switch. As liquid lowers to the trigger point of the first stage, the pump is activated. If the liquid continues to drop (perhaps because the pump has failed, its supply has been cut off or exhausted, or its discharge is blocked), the second stage will be triggered. This stage may switch off the boiler equipment (preventing the boiler from running dry and overheating), trigger an alarm, or both.
Another common form of feedwater pumps run constantly and are provided with a minimum flow device to stop overpressuring the pump on low flows.The minimum flow usual returns to the tank or deaerator.

Steam-powered pumps

Steam locomotives and the steam engines used on ships and stationary applications such as power plants also required feedwater pumps. In this situation, though, the pump was often powered using a small steam engine that ran using the steam produced by the boiler. A means had to be provided, of course, to put the initial charge of water into the boiler (before steam power was available to operate the steam-powered feedwater pump). The pump was often a positive displacement pump that had steam valves and cylinders at one end and feedwater cylinders at the other end; no crankshaft was required.

 

 

0 Steam Turbine

Why are they used for CHP?

Steam turbines have been generating electricity in America for years. Power generated by steam turbines have been the first light bulb and encourage our ships for over 100 years. In fact, the first power plant (run by Thomas Edison to use a dynamo and is located in Pearl Street in New York City) is a CHP plant that generated electricity by using steam turbine. Excess steam used to heat homes. Today, most electricity produced in the United States to do so by a steam turbine. It is safe to say steam turbine technology is well known, well understood and proven.

Because the steam turbine run away from the steam produced by the boiler, it can support many various types of fuel. Natural gas, coal, nuclear, wood, municipal solid waste and more all can be used to run steam turbines. As a result, facilities that have excess waste products such as oil or wood tends to apply the steam turbine. As the picture below show, this time the steam turbine CHP system is run from a variety of fuels.

Another interesting feature of steam turbines is that they can be modified to fit any CHP system. Therefore, the steam turbine can be installed to match the pressure of the facility and temperature requirements. Furthermore, the steam turbine can be retrofitted into existing steam system. Furthermore, water and steam is very well understood. Using the steam table, we can know the exact nature of our working fluid at a given temperature and pressure. Therefore, the steam is very predictable.


Technology brief description:
 
Steam turbine is slightly different from other CHP prime mover in that they require separate boiler or "HRSG" (Heat Recovery Steam Generator) to make the working fluid (Steam). Sometimes, the plant will already have a boiler for the production process or to meet the burden of heating / cooling and instead of using "pressure reducing valve" for "Isenthalpically" reduce the vapor pressure, they will be running the steam through "Back pressure steam turbine" and generate electricity. In CHP applications, boiler or HRSG to generate steam that will be put through a steam turbine. steam turbine will produce electricity and steam exhaust the remaining can be used for hot water or heating / cooling.

The process of steam generation is the basis behind the "Rankine cycle". water heated to saturated liquid. From there, it is compressed into steam. steam transferred to a steam turbine where the pressure is reduced (typically to sub atmospheric pressure) by expansion over the turbine blades. This process produces
electricity. Low pressure steam is condensed back to liquid. The water, now called as the return of water, mixed with new water, referred to as "bait", and pumped back to the boiler. The figure below shows a diagram commonly used to describe the Rankine Cycle.

There are three types of steam turbines: condensing, non-condensing, and extraction. Condensing turbine is not used for CHP applications and therefore will not be discussed here. Non-condensing steam turbine is also referred to as "back pressure" steam turbine. Here, the expanded steam for steam and gas turbine exhaust is used to meet the needs of the steam facility. Expanded until it reaches the steam pressurefacility may be used. The figure below, taken from NREL, the schematic shows the process back pressure steam turbine.

Other types of steam turbines used in CHP applications is called extraction turbine. In the turbine, the steam extracted from the turbine at some intermediate pressure. this Steam can be used to meet the needs of the steam facility. The remaining steam expanded more and thicker. Extraction turbines can also act as a turbine inside. in entry turbines, steam turbines are added to the medium at some point. The figure below shows the process scheme of an extraction steam turbine.


Waste heat from the steam turbine (either collected through the exhaust or from the extraction), can be used to heating or cooling chamber, to process, or can be used to make a cold or  hot water. Steam turbine can also be part of the "combined cycle". In  process, the waste steam from electricity production process (ie waste generated steam  by gas turbines) is run through a steam turbine to generate more electricity. While this  very energy efficient, does not consider the CHP because there is no heating or cooling load is satisfied in each section. 

Steam system efficiency is difficult to calculate. 40-50% is a number that is usually attached to the steam turbine efficiency. However, this number can be misleading because it does not take into account boiler efficiency. Boilers are usually 80-85% efficient. If such a boiler is included in the steam system, then the efficiency of steam system drops to 32 to 42.5%. However, if the boiler is already in place and steam turbine was added later, then the general efficiency of the boiler does not need to be considered. Another thing to consider is if back pressure steam turbine replaces the pressure reducing valve or steam blow from practice, then any energy you can get is the energy efficient. The reason behind this is that the plant well before energy loss by expansion isenthalpic or just blow off excess steam. Now, these plants use of energy and therefore, when compared with the previous, more energy crops efficient.

cost:
Steam turbine boiler plus installation costs between $ 800 - $ 1000/kW. If the boiler is already in place, just a steam turbine installation cost alone is $ 400 - $ 800/kW. Maintenance costs for an estimated $ 0.004/kWhr steam turbine. steam turbine has been known to last more than 50 years with more than 99% availability. Table 1 gives the cost info for steam turbines only.
 
emissions:
Steam turbine does not emit anything themselves. However, emitting steam generator pollutants. Therefore, the emissions from a steam turbine system is highly variable and depending on the type of fuel used to create steam and the method by which steam made. Boiler will emit NOx, SOx, PM, CO, and CO2. Typical boiler emissions shown in the following table.

There are a variety of emission control technology for steam systems. Some These include: Flu-gas recirculation, low excess air firing, combustion control, using low nitrogen fuel oil, enter the water / steam to reduce NOx, non-selective catalytic reduction, selective catalytic reduction and others.