What is the cheapest source of renewable energy ? - Biomass

The conventional energy sources are rapidly depleting because of their excessive use in the modern world. And that's why energy or power generation sectors are very much interested in the utilization of renewable energy sources. The conventional energy source includes Natural Gas, Coal, Nuclear Energy, Crude oil etc. The price of these non-renewable fuels is almost touching the sky and getting closer every day. But the price of utilization of non-conventional energy source is not very cheap either. Cheap renewable energy source promises a greater power generation with a cleaner environment.

Please Read : Different Renewable Energy Sources 

Expensive Conventional Energy Sources

Crude Oil

According to Brent Crude Oil the price of one barrel oil was $116! Yeah that’s right and yet oil is expected to remain the predominant source of energy production! The demand of oil will increase by 1.7% in the year of 2025 because of the energy consumption in USA and developing Asia. So it is high time we should look forward for a cheap reliable energy source. 

Natural Gas

Another very attractive non-renewable fuel is Natural Gas. According to the estimation the use of natural gas will be increased by 67% by the year 2025. And therefore the consumption of Natural Gas will be 151 trillion cft. If the consumption increases in that rate then it can be predicted that the life of Natural Gas will be very short on The Earth. 

Coal 

70% Steel production companies uses coal as fuel. 38% of the world’s electricity generation comes from coal. It has high calorific value but at the same time very detrimental to the environment. The high quality coal comes in exchange of a high price!

Nuclear Energy

Uranium is the main fuel for producing energy by nuclear fission reaction.  U₂₃₅ is the primary fuel for nuclear power generation. According to World Nuclear Association the price of 1 kg Uranium stands US $2360 (After conversion enrichment, fabrication)! And it is only the operating cost!

Capital cost + Plant operating cost + External cost = $5300/kW!

Please Read: Different Types of Nuclear Reactors with their Working Principles

Expensive Non-conventional or Renewable Energy Sources

Solar Energy

Sun is the source of energy. The energy from the sun in 19 trillion toe (Ton of Oil Equivalent)/year. And the world’s energy consumption is only 9 billion toe. So a fraction of sun’s energy can fulfill the energy needs. Sun’s energy is extracted mainly by solar collectors. Photovoltaic Cells (PV) are used to store the energy from sun. A single solar panel for household use can cost up to $35000 according to the power output. And this cost does not account the taxes, battery and installation cost! So clearly it is not the cheapest source.

Wind Energy

We get wind because of the pressure difference on the different areas of the earth. The air moves from high pressure to low pressure area and it causes the wind. Wind energy is actually derived from solar energy because Sun heats the earth and creates temperature differences. Hot air expands and rises up and cool air near the oceans rushes and fill that space. That’s how air is circulated. Wind energy potential is not available for use in all the places. Energy density and normality depends on geographical locations. Wind energy is very erratic and irregular. Wind turbine design is very complex and needs a good investment. To create a large plant based on wind turbines, capital intensive technology is needed.

Geothermal Energy

The interior of the earth is full of molten materials. The inner core has solid materials and the outer core is filled up liquid rock named Magma (4000 degree Celsius). Geothermal resources can be divided into this two parts –

•      Liquid dominant resource, which involves

1.        Flash steam power plant 
2.        Binary Cycle Power Plant

•      Vapor dominated resource.

Though geothermal energy is a very good potential source, it has some limitations. Geothermal energy is available in the geothermal sites only.

Ocean Energy

It is kind of hydro energy but it is mainly derived from Thermal radiation of the sun. The surface water of the ocean is heated but the deep ocean water still remains cool. These temperature difference can be used to get OTEC (Ocean Thermal Energy Conversion). From the 19^th century scientists are trying to make this plant work but it is not that popular because of the high cost of the plant. It needs very large diameter pipe which is needed to be submerged a kilometer or more than that to get the cool water.

Cheap Non-Conventional Energy Source

Hydropower source – Tidal Energy

Hydro power can be got from tides and waves. Tidal power plant needs mechanical equipment. This energy is mainly due to the pull of moon.

It can be

•          Single basin single tide
•          Double basin single tide
•          Double basin with the power house in the separating dam.

 It can be proved very useful for the countries having large water reservoirs. The fuel cost is absolutely nil. But the erection of this type of plant can take years. And the rate of return is very low. So the plant owners or government can suffer, running this type of power plant. But it is one of the cheapest source of renewable energy.

Please Read : Advantages and Disadvantages of Hydroelectric Power 

Biomass

According to my studies I think Biomass is the most potential source for energy production. It can be got from forest areas, agricultural residues, Urban wastes, Industrial wastes and natural vegetation.

Biomass – The Cheapest source of Renewable Energy

Yes, I would say biomass because it can use aquatic crops, vegetable oil crops, and animal wastes even human wastes for fuel production. Every day almost 42 million tons of solid waste and 6000 million cubic meters of liquid waste are generated in urban areas. What you will do with all these huge waste materials? If these are utilized to produce power than it would be much better for our environment. And these waste materials are not expensive for sure. Biomass can provide us with biofuels and biogas.

Biofuels

Charcoal – These possess high energy density and can be burned at temperatures high as 600 degrees. Very good for household, commercial and industrial uses.

Briquetting – It can be produced from coconut shells, saw dust, wood chips etc. This are made into high density fuel element.

Vegetable oils – Palm, coconut, cotton, rapeseed and soybean oils can be used as bio fuels. These can mixed with diesel to form premium grade fuel.

Biogas –

Biogas can be produced from digestion of the waste materials like human waste, animal waste and plant waste.  Biogas is mixture of Methane, Carbon dioxide, Hydrogen, Hydrogen Sulfide and Nitrogen. Here Methane CH₄ is predominant (55 -65%). Methane is very clean burner.

Biogas Plants are also very cheap to fabricate. There are two very popular designs to produce biogas

       

•         Floating Drum Biogas Plant (KVIC model) or Chinese Biogas Plant
•         Fixed Dome Type Biogas Plant (Indian Biogas plant design, Janata Model)

Biodiesel

Biodiesel can be produced by mixing organic oil with diesel. Non-edible oil seeds are much preferred for the production of the oil. These produces very small amount of CO₂ and zero sulfur. These fuels have very high flash points so they are easily transported without any danger of self-ignition and combustion. This fuels give high octane ratings. Biodiesel can be produced from Jatropha Curcus, Jojoba, Sunflower, and Soybean and also from peanut. Amongst them Jatropha is the cheapest. It is economically favorable and it costs $0.08/kg of seeds! Where Jojoba seeds costs $3.39/kg.

So Biomass derivatives – biofuels, biogas and biodiesels are the cheapest source of renewable energy.

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Condenser Classification – De-aeration of Condenser

What is Condenser  ? 

The primary purpose of the condenser is to condense the exhaust steam from the turbine and thus recover the high-quality feedwater for reuse in the cycle.

In order for a steam power station to operate an efficient-closed cycle, the condensing plant, cooling water (CW) system, and associated pumps must extract the maximum quantity of heat from the exhaust steam of the LP turbines

The primary functions of the Condensing plant are:

·         To provide the lowest economic heat rejection temperature for the steam cycle

·         To convert the exhaust steam to water for reuse in feed the cycle

·         To collect the useful residual heat from the drains of the turbine feedheating plant, and other auxiliaries. 

·         In so doing, the circulating cooling water temperature being low enough, it creates a low back pressure (vacuum) for the turbine to exhaust to. 

·         This pressure is equal to the saturation pressure corresponds to the condensing temperature which is a function of the cooling water temperature. 

·         Since the enthalpy drop and hence turbine work, per unit pressure drop is much greater at low pressure than the high pressure end of the turbine. 

·         The condenser, by lowering the back pressure a little bit increases the work of the turbine, increases the plant efficiency, and reduce steam flow for a given output 

·         The lower the pressure, the greater the effects

Condensing power plants are, therefore, much more efficient than non-condensing ones.

(Why Condensing power plants are much more efficient than non-condensing ones, I think you got the answer)

Some other functions of Condenser: Additional Condenser Objectives

In addition to the condenser satisfying the primary functions, its design must also be capable of meeting the following objectives:

·         To provide the turbine with the most economic back pressure consistent with the seasonal variations in CW temperature or the heat sink temperature of the CW system.

·         To effectively prevent chemical contamination of the condensate either from CW leakage or from inadequate steam space gas removal and condensate de-aeration.

·         The aim of the designs is to ensure that these objectives are met within the framework of the following practical considerations:

 i. Economies of size, space and pumping power

 ii.  Ease of maintenance and construction

 iii. An economical turbine back pressure is from 1.0 to 3.5 in Hg abs

Classification of Condensers: 

• There are two broad classes of condensers:

Direct contact type condensers — the condensate and CW directly mix and come out as a single stream

Surface condensers — are shell-and-tube type Heat Exchanger where the two fluids do not come in direct contact and the heat released by the condensation of steam is transferred through the walls of the tubes into the cooling water continuously circulating inside them. 

Direct Contact type condenser

When low investment is desired and condensate recovery is not a factor, direct-contact condensers are effective.

They are relatively simple to build and operate, are limited to sizes less than 250,000 lb. (114 tons) of steam per hour 

Direct Contact type condensers can be of three types:

·         Spray condenser

·         Barometric condenser

·         Jet condenser

 Direct Contact Spray Type

·         In a spray condenser the cooling water is sprayed into the steam which by mixing directly with cold water gets condensed.

·         Part of the condensate, equal to the turbine exhaust flow, is sent back to the plant as feedwater. 

·         The remainder is cooled in a dry cooling tower to state 5 and is then sprayed on to the turbine exhaust thus, the cooling water continually circulates.

Direct Contact Barometer Type 

·         The cooling water is made to fall in a series of baffles to expose large surface area for the steam fed from below to come in direct contact.

·         The condensed steam and the cooling water mixture falls in a tail pipe to the hot well below the tail pipe compresses the mixture to atmospheric pressure at the hot well by virtue of its static head

Direct Contact Jet Type 

·         In the jet-type Condenser the height of the tail pipe is reduced by replacing it with a diffuser

·         The diffuser helps raising the pressure in a short distance than a tail pipe

·         In all direct contact Condensers the non-condensable gases must be removed which is usually done with a steam-jet air ejector (SJAE)

Surface Type Condensers

·         Surface Condensers shell and tube heat exchangers are mostly used in power plants

·         For the convenience of cleaning and maintenance cooling water flows through the tubes and steam condenses outside the tubes

·         Present-day condensers have heat transfer surface areas that exceed 1 million ft2 (93000 m2)

·         Condensers are designed with one, two, or four water passes.

·         The number of passes determines the size and effectiveness of a Condenser.

Single Pass Condenser 

In an A single-pass condenser cooling water flows through all the Condenser tubes once, from one end to the other.

Two Pass Condenser

In Two-pass condenser water enters half the- tubes at one end of a divided inlet water box. And then passes through these tubes to an undivided water box at the other end. Then they reverse direction and passes through the other half of the tubes back to the other side of the divided water box.

Single Pass Condenser should be used or two pass? 

A single-pass condenser with the same total number size of tubes, i.e., the same heat-transfer area, and same water velocity, requires twice as much water flows but results in half the water temperature rise and thus lower condenser pressure

Thus such a single—pass condenser is good for plant thermal efficiency and reduces thermal pollution, but requires more than twice the water and hence four times the pumping power

Water boxes are often divided beyond the divisions required by the number of passes

A divided water box single-pass condenser may have a partition in both the inlet and outlet water boxes at opposite ends of the condenser — allows half the condenser to operate while the other half is being cleaned or repaired. 

Divided water boxes have duplicate inlet and outlet connections, each with its own circulating water circuit. 

Many large modern-day power plants usually have two or more low-pressure turbine sections in tandem.

The condenser may be divided into Corresponding sections or shells.  

Single Pressure Condenser

When the turbine exhaust pressure in all sections is same, i.e. when the exhaust ducts are not isolated from each other, it is known as a single-pressure condenser. 

Multi-Pressure Condenser

If the exhaust ducts are isolated from each other, these individual condenser shell pressures will increase because the circulating water temperature will increase as it flow from shell to shell — a multi-pressure condenser

Why multi pressure condenser is preferable than single pressure condenser?

A multi-pressure condenser results in efficiency improvement because the average turbine back pressure is less compared with that of a single-pressure condenser (Which is determined by the highest circulating water temperature)

In essence, condensers are almost custom designed to suit individual requirements of steam flow available cooling water flow and temperature, available space and other variables. 

Surface Type Condenser Design Considerations

A condenser design can be established for a given performance rating based on eight principal variable which are

·         Total heat transferred, which is a function of 

Ø  Weight of steam to be considered.

Ø  Enthalpy of steam less enthalpy of condensate. 

Ø  Enthalpy loss or gains of drains and make up. 

·         Absolute static steam pressure.

·         Cooling water flow rate

·         Cooling water inlet temperature.

·         Cooling water outlet temperature.

·         Cooling water velocity through tubes.

·         Effective heat transfer surface, which is a function of:

 Ø  Number of tubes
Tube length
Tube diameter
Tube thickness
Tube material
Number of cooling water passes

Ø  Service conditions:

o   Tube cleanliness

o   Air in-leakage

The tube material can be:

Cupronickel (70% Cu, 30% Ni)
Aluminum brass (76% Cu, 22% Zn. 2% AI
Aluminum bronze (95% Cu, 5% AI)
Muntz metal (60% Cu, 40% Zn)
Admiralty alloy (71 % Cu, 28% Zn, 1 % Sn)
Stainless steel

De-aeration or Air Removal of condenser
 

Air may leak into the condenser shell through flanges or sometimes comes along with steam which has leaked into the exhaust end of the turbine along the shaft

This air affects the condenser performance badly because of the following reasons:

·         It reduces the heat transfer considerably

·         It reduces the condenser vacuum and increases the turbine exhaust pressure thus reducing the turbine output

 Good de-aeration within a condenser requires time, turbulence and good venting equipment

·         The cold condensate falling from the lower tubes must have sufficient falling height and scrubbing steam for reheat and de-aeration

·         The scrubbing steam is provided by allowing some of the incoming steam to pass through an open flow area directly to the bottom tubes to reheat the condensate — non condensable are more easily released from a hotter than a colder liquid.

·         Once the non-condensable are released, they are cooled to reduce their volume before being pumped out of the condenser

·         For this a number of water tubes, about 6 to 8% in the tube bundle, are set aside for this function. 

·         This, called an air-cooler section, is baffled to separate the non condensables from the main steam flow

·         Most of the condensation takes place on the main bank of tubes and the air is drawn over another smaller bank which is shielded from the main bank by a baffle and is called the a aircooler. 

·         Here, further condensation takes place at a lower temperature and thus, there is saving in feedwater as well as in air ejection load.

·         Jet pumps are used to pump out the non-condesables — known as steam jet air ejectors (SJAE)

Ø  In a two-stage ejector, main steam is used at a reduced pressure that enters a driving nozzle in the first stage ejector

Ø  It exits with a high velocity and momentum and reduced pressure

Ø  This reduced pressure draws in the non-condensables from the condenser

Ø  By a process of momentum exchange, the gases are entrained by the steam jet

·         The combined flow of steam and gas is now compressed in the diffuser of the first-stage ejector and discharged into a small inter-condenser, where the steam is condensed by passing across cooling pipes in much the same manner as the main condenser.

·         Cooling here, however, is accomplished by the main condenser condensate and is part of the feedwater heating system, resulting in improvement in efficiency of the plant.

·         The non-condensables and any remaining steam are then passed to the second stage ejector, where they are compressed further and passed to an after-condenser

Vacuum efficiency of a Condenser

Sometimes a term called ‘Vacuum efficiency’ is often used a regard to a condenser

It is defined as:

Vacuum efficiency = (Vacuum produced by steam condenser inlet/Barometric pressure - Saturation pressure at exhaust steam pressure)

Condenser efficiency

Another term called ‘condenser efficiency’ is also used sometimes.

Which is defined as:

Condenser efficiency = (Actual temperature rise of cooling water/Maximum temperature rise of cooling water)

Read :

• Hydroelectric Power Plant facts with merits and demerits 
• Flash Steam Power plant running by Geothermal Energy 
• Different Types of Nuclear Reactors with schematics 
• Renewable energy sources 

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Advantages and Disadvantages of Hydroelectric power - Facts

What is hydroelectric power (facts) ? 

Let’s start with the hydroelectric power definition:

In hydroelectric power plants, the potential energy of water is converted into mechanical energy which runs a generator.

• Hydraulic power is a naturally available renewable energy source. 

• Power of a hydroelectric power station is given as: P = gρQH watts 

• Where g = 9.81 m/s², p = 1000 kg/m³, Q is the flow or discharge in m³/s, and H is the height of fall of water or head in m. 

• The efficiency of the turbine-generator assembly in a hydroelectric power plant usually varies between 50% and 90%.

• Almost 20% of the total power requirement of the world comes from hydro power

• Countries like Norway and Switzerland are almost totally dependent on hydropower.

Advantages and disadvantages of hydroelectric power

Advantages of Hydro power plants : 

Hydro power has a number of advantages:

• Water source is always available – no extra fuel is needed to be used to produce electricity

• The running costs of hydro power installations are very low.

•  Hydro power is environmentally benign.

•  The operation of Hydraulic turbine can be started or stopped in very short time.

• The hydraulic power plant is comparatively simple in concept and design.

• The operation of hydroelectric power plant is self-reliant.

• Hydro power stations are much more reliable in comparison with other power plants. 

• Modern hydro power equipment has a life of nearly 50 years.  With extraordinary maintenance the life can be increased to more than 50 years. 

• Hydroelectric plant can handle the load very easily and thus they can be used as the ideal spinning reserve in an electrical system. 

• Modern hydro-generators give high efficiency as well as handle a considerable range of load which helps improving the overall system efficiency. 

•  Manpower requirement is low; also the manpower need not be highly skilled

• The extra or bonus advantages of hydroelectric power are - they provide the means of irrigation and also contributes in flood control etc.

Disadvantages of Hydro power plants

The disadvantages are:

• Cost of hydroelectric power is a matter of great concern. Hydropower projects are capital intensive with a low rate of return

• Annual cost of hydropower installations takes a big part of the annual interest of the capital.

• The growth period of hydroelectric power projects s quite large

• The foundation and completion of a hydro power project is very hefty.  Ten to fifteen years may be needed to complete the project.

• Power generation is totally dependent on the quantity of water available, which may vary from season to season and year to year.

• These plants are often far away from the load center (most of the time in remote areas) and require long power transmission lines to deliver power — thus the cost of transmission lines are very high as well as losses in them are very significant.  

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Renewable Energy Sources - Graphical Presentation

 What are renewable energy sources ? 

Renewable Energy Sources refers to the sources which are not at risk of being finished. They are replaced naturally. At present times it seems that the use of renewable sources are inevitable because the non - renewable energy sources are getting scarce. The non-renewables like coal, crude oil. nuclear sources, natural gas, wood fuels, shale oil are almost on the verge of getting totally finished. So power industries are now looking for the utilization of the renewables. At present 16% of the world's total energy supply comes from renewable sources.

• A schematic representation of Flash Steam Power plant powered by Geothermal Energy
• Different Energy Sources - Units and Conversions

Renewable energy sources list

The main sources for renewable energy are 

• Solar Energy (Photovoltaic Cells , PV)
• Wind energy 
• Ocean Energy (Ocean Thermal Energy Conversion , OTEC and Wave energy)
• Tidal energy 
• Geothermal Energy 
• Hydraulic Energy sources 
• Energy from Biomass etc . 

Here is a Graphical representation of the energy sources.

Characteristic Features of Renewable Energy Resources-

I will like to give some information about the most used renewable sources. 

Biomass

Biomass generation is- Micro power also known as on-site generation and distributed generation. It is also known as small-scale generation and it has the ability to self-generation, etc. By using biomass plants we can get a cleaner environment. 

 The New concpet of Tri-generation could potentially bring a lot of  benefits to many remote village areas . Rural scale tri-generation is based on gasification of different crop residues. Use of micro turbines for CHP can be proved very beneficial for the economic developments and meeting power requirements.  

Other Renewables

In a report by Shell Renewables, a part of one of the world’s largest oil companies — When we will reach the year 2050,  half of the world's energy consumption will come from solar and other renewable sources. 

Every year, we get an equivalent of 19 trillion toe (tons of oil equivalent) from the Sun's radiation. A fraction of this energy will be able to satisfy the world’s energy consumption which is  around 9 billion toe per year.

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How to Solve Fluid Mechanics Problems Using Moody Diagram

Hello my fellow science lovers and Mechanical Engineers. Today I am gonna solve an example problem of Fluid Mechanics or Fluid Power (Fluidics) using Very Important Moody Diagram. Before you start to look at the problem you can have a look at the following post - 

• How to Use Moody Diagram 

Problem Solving Using Moody Diagram 

Problem -   A Hydraulic oil has the kinematic viscosity of 50 cS . The oil flows through a commercial steel pipe of 1 inch diameter. Find the friction factor for the following conditions -

a. Velocity of the flow - 10 ft/s 

b. Velocity of the flow - 40 ft/s 

Solution 

At first we have to find Raynolds Number from this formula, (This formula is optimized for kinematic viscosity in cS = Centistokes)


N_{R  
=} 

₌ 

Putting the values of all the parameters we get - 

a . Raynolds Number is 1548. So the flow is laminer (Raynolds number < 2000 )

 So here we don't need the relative roughness and hence we don't need the Moody Chart. Simply we will use the formula  for friction factor, f 

By using this formula we get friction factor , f = 0.042 (ans)

b. Raynolds Number is 6192 . So the flow is Turbulent (Raynolds Number > 4000)  

Now for turbulent flow we will have to use moody diagram for getting the friction factor. For that reason we have to calculate the relative roughness. Here is the equation for relative roughness.

For getting the value of epsilon we will use this chart -

From the chart we see that-  for commercial steel actual roughness epsilon = 0.0018 

So Relative roughness = 0.0018 in / 1 in = 0.0018 

Now get  in to the moody chart 

Locate Raynolds Number = 6192 in the Raynolds Number axis in the chart. And now go up vertically to get the value of relative roughness = 0.0018 . Now project horizontally for getting the value of f . Which is f = 0.036 (ans) . For your assistance the necessary points are shown in the diagram.

Thank you. If you have any question about the problem or the Moody Diagram then contact me or just leave a comment. Cheers ! Hope this will be helpful .

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