BOILER DESIGN

Efficiency of a boiler is the result of its basic heat transfer design. Boiler designs that use all possible heat transfer surfaces to their fullest advantage consistently produce the most efficient source of steam or hot water with the lowest total lifetime costs.
SOFTWARE FOR FIRE-TUBE & WATER-TUBE BOILERS
Softwares are based on new theoretical findings on heat transfer in boilers. It delivers unprecedented proven +/-2% uncertainty. It can be used to carry out tasks like:
•    heat transfer analysis in boilers
•    boiler design optimization
•    retrofit of installed boilers.
Software calculates heat transfer in fossil fuel fired fire-tube and water-tube steam, hot water and waste heat boilers of arbitrary geometry and for arbitrary operating conditions (excess air, pressure up to 99bar/1435psi). Boiler can consist of multiple segments such as furnace, channels, chambers and tubes, with or without front or/and rear cooled door. The boiler segments can be combined, which makes calculation of next to every known boiler design possible.
Water-tube boilers are in essence of relatively simple basic design consisting of a large rectangular combustion chamber while fire-tube ones come in various designs. Following fire-boiler designs can be calculated with the software:
1. Tubular boiler
•    single pass or double pass
•    horizontal or vertical
•    tubes can have coiled-wire turbulators or dents.
2. Furnace (combustion chamber)
•    circular or rectangular
•    horizontal or vertical
•    with or without rectangular fins
•    wetback or dryback
•    with or without front cooled door.
3. Channel after furnace (if any)
•    one or more
•    circular or rectangular
•    horizontal or vertical
•    with or without rectangular fins
•    with or without baffles.
4. Boiler with 1, 2 or 3 tube assemblies after furnace (2-pass, 2-pass reverse flue, 3-pass, 4-pass)
•    horizontal or vertical
•    tubes can have coiled-wire turbulators or dents.
5. Redirection channel between two tube sets (one in 3-pass and two in 4-pass boilers)
•    circular or rectangular
•    horizontal or vertical.
6. Channel before boiler exit (if any)
•    one or more
•    circular or rectangular
•    horizontal or vertical.
7. Boiler with cooled rear door.
8. Waste heat boiler or exhaust gas boiler (such as hybrid biomass system) without or with supplemental firing .
9. Tubular economizer with or without fins (circular or rectangular). Can also be calculated separately as can stoichiometry of combustion.
Boiler can be made of following materials:
•    boiler steel
•    cast iron.
Economizer tubes can be made of following materials:
•    steel
•    copper.
Boiler liquid can be following:
•    water
•    Rankine cycle liquid
•    thermal oil.
Input and output values can be either in Metric or English units.
Order of calculations
1. A stoichiometry of the combustion, adiabatic combustion temperature, flue-gas enthalpy at that temperature, and a first estimation for the furnace exit temperature are calculated.
2. Convective and radiant parts of the heat transfer are considered to be simultaneously coexistent. For convection, the relevant temperature is mean logarithmic, for radiation the mean radiant temperature that is calculated by proprietary procedure.
3. The impact of the turbulators or tube dents is taken into account according to the proprietary developed procedure.
4. The convective and radiant parts of the heat transfer in the furnace are summed-up and deducted from the flue gas enthalpy at the adiabatic combustion temperature. The result is a temperature at the furnace exit.
5. The calculated flue-gas exit temperature is compared to the estimated one in step 1. If they do not meet the preset difference (0.1°C) a new estimation is calculated as the average of assumed one in step 1 and just calculated one. The procedure is then repeated.
6. This same procedure is applied to every boiler segment using the exit temperature of flue gas from one segment as being the initial temperature in the next section. Thus, the initial temperature in next boiler section is equivalent to the exit temperature from preceding section.
7. The sum of the heat transferred in all boiler sections represents its heat output which, when divided by heat released from fuel, yields the boiler efficiency.
Discrepancy sources between measured and calculated values
There are always differences between calculated and actual values. The discrepancies are of an operational (fouling, scaling on gas and water side) and of mathematical nature (heat transfer equations are always derived from experiments). In general, for new and well maintained boilers the discrepancy to actual values is as low as 2% (boiler output, steam capacity, efficiency).
Heat balance for a boiler
Fuel fed to a burner is converted to heat. The heat is absorbed by the water in the boiler, but not all the heat released from the fuel is used to heat the water. Some of the heat is wasted in the process. The heat balance of a boiler consists of accounting for all the heat units in the fuel used or wasted. It is a balance because it is the sum of all the heat consumed. Heat balance of a boiler is found by using the following equation:
A = B + C
A= heat energy available in the fuel
B= heat energy absorbed any the water in the boiler
C= heat losses
Therefore: Efficiency of the unit = B divided by A
Energy losses in a boiler
􀂃 Gases of combustion to atmosphere (about 9%)
􀂃 Incomplete combustion (about 1%)
􀂃 Moisture in fuel (less than 1%)
􀂃 Moisture in air used for combustion (less than 1%)
􀂃 Water vapor produced from the burning of hydrogen (about 2%)
􀂃 Unburned combustibles (about 2%)
􀂃 Radiation (about3%)
Total heat losses in this examples equal 18-19% While some of these losses are preventable losses over which the boiler operator has control, such as:
􀂃 Heat carried away in the dry chimney gases
􀂃 Incomplete combustion of the fuel
􀂃 Unburned combustibles (about 2%)

New batteries

The new batteries can withstand extremely high rates of charge and discharge which will cause electrodes used in conventional Li-ion batteries to rapidly deteriorate and fail. The greatest advantage of the new batteries is that charging laptop or cell phone in a few minutes, rather than an hour.
Construction
The new batteries are made from a carbon (C) nanorod base topped with a thin layer of nanoscale aluminum (Al) and a "scoop" of nanoscale silicon (Si), the structures are flexible and able to quickly accept and discharge Li ions at extremely fast rates without sustaining significant damage. The segmented structure of the nanoscoop allows the strain to be gradually transferred from the C base to the Al layer, and finally to the Si scoop. This natural strain gradation provides for a less abrupt transition in stress across the material interfaces, leading to improved structural integrity of the electrode.
Charging cycle
The anode structure of a Li-ion battery physically grows and shrinks as the battery charges or discharges. When charging, the addition of Li ions increases the volume of the anode, while discharging has the opposite effect. These volume changes result in a buildup of stress in the anode. Too great a stress that builds up too quickly, as in the case of a battery charging or discharging at high speeds, can cause the battery to fail prematurely. This is why most batteries in today's portable electronic devices like cell phones and laptops charge very slowly, the slow charge rate is intentional and designed to protect the battery from stress-induced damage. Due to their nanoscale size, nanoscoops can soak and release Li at high rates far more effectively than the macroscale anodes used in today's Li-ion batteries.
Limitation
A limitation of the nanoscoop architecture is the relatively low total mass of the electrode, according to the researchers and to solve this, the researchers are to trying to grow longer scoops with greater mass, or develop a method for stacking layers of nanoscoops on top of each other or to grow the nanoscoops on large flexible substrates that can be rolled or shaped to fit along the contours or chassis or chassis of the device.
The nanomaterial for a new breed of high-power rechargeable lithium (Li)-ion batteries has been  developed at Rensselaer Polytechnic Institute.

About biomass conversion technologies

Biomass composition
Biomass fuels consist of three main segments: wood, waste, and alcohol fuels. Wood energy is derived from the following sources: round wood, used primarily in the industrial and electric utility sectors; wood fuel, used predominantly in the residential and commercial sectors; and wood byproducts and wood waste, which are usually used in the industrial sector. The chemical composition of plant biomass varies among species and has approximately 25% lignin and 75% carbohydrates or sugars linked together in long chains or polymers as cellulose and hemi-cellulose. The lignin fraction consists of non-sugar type molecules that act as a glue holding together the cellulose fibers.
Biomass categories
• Solid Biomass, which includes tree, crop residues like rice husk, bagasse, coconut shells, jute waste, etc. and animal and human waste.
• Biogas which is obtained by anaerobically digesting organic material to produce combustible gas methane.
• Liquid biofuels which are obtained by subjecting organic materials to one of various chemical or physical processes to produce usable combustible liquid fuels.
Conversion methods
A number of technological options are available to make use of a wide variety of biomass types as a renewable energy source. Conversion may release energy directly in the form of heat/electricity or, may convert it into another form such as liquid biofuels or combustible biogas. There are basically three types of conversions:
• Thermal Conversion- A process in which heat is used to convert biomass into another chemical form.
• Chemical Conversion – A range of chemical processes may be used to convert biomass into other forms so that fuel may be used more conveniently, transported or stored.
• Biochemical Conversion- It involves anaerobic digestion fermentation and composting.
Gasification technology
Gasification is one of the most promising technologies in biomass applications particularly because of higher efficiency compared to boiler power systems, amenability to fuel synthesis and environmental friendly features. Biomass gasification has evolved over a long period, but it has not reached a solid commercial stage, except during periods of crises and only for some specific applications while, other gasification technologies, fed by fossil fuels, are currently widely used on industrial scales.
Historical evolution gas plants
The first producer gas plant was designed around 1850. After 1880 the technology found wider application. Producer gas plants used during the First World War were very well described in the literature. The application of small gasification systems for traction assumed enormous proportions by the end of Second World War. Approximately 1 million vehicles were powered by wood blocks, peat, charcoal or anthracite. When oil and gas took over the predominant part of coal and wood, the development of producer gas plants was limited to countries with exceptional local circumstances, such as South Africa where large pressurized Lurgi plants were in operation. It was only around 1970 that attention was paid again to small scale gasification of biomass especially in remote areas of developing countries. Some year’s later research and development programmes were initiated as a result of the energy crisis and concern for the environment. Many conference papers and workshop document these activities and present a good survey on recent research and development on biomass gasification.
Combustion in a controlled atmosphere is the conversion of solid or liquid to a gas. If the oxygen supply is restricted, incomplete combustion of fuel occurs releasing combustible gases such as CO,H2 and CH4. Investigations on Gas producer-Engine systems, a century old technology and forgotten art, have experienced renewed interest in recent years. More than 12000 gas producer plants were in operation in the United States and Canada during the 1920s and 1930's.
Austria, Finland, Germany and Sweden have increasing number of ongoing projects and initiatives since 1970. The development of this technology has been encouraged by the price of fossil fuels and an enhanced interest for biomass gasification as a future alternative. But this technology has not sufficiently achieved a sustainable commercial status. Experimentation activities, demonstration projects and pilot plants, have proved the future potential of the technology.
Small and large scale projects have followed different development routes. In the case of large scale, interest has shifted from electricity generation to biofuel production, primarily due to the failed demonstration projects of the technology coupled with combined cycle for electricity generation. On the other hand, in small scale projects, cogeneration applications have gained interest over heat production. Also in small scale experimentation the causes which have hindered the technology to reach the expected commercial stage has been the lack of resources to demonstrate its competitiveness. Objectives of achieving the success of gasification technology will depend on incentives created by all administrative levels.
Power generation modes
Biomass is a renewable source of energy that can be made use of effectively for thermal as well as electrical energy generation. The biomass based power plants are of smaller capacity, usually situated either at agro-based industries, where the biomass is generated or at a place where crop residue or other type of biomass is located. This decentralized power plant will help in supplying quality power and reduce the transmission and distribution losses. Biomass based power plants can either be as cogeneration or as independent power plant.
Cogeneration
Cogeneration is defined as generation of process heat and motive power by the sequential use of energy from a common fuel source. This is an energy efficient technology as it utilizes the low grade exhaust heat from the steam turbine for process heating. This enhances the efficiency of energy utilization from 35% in the conventional power generating system to 70-90% in the co generating system.
Combustion
Combustion route is an established and reliable system to generate power from biomass. This system consists of boiler, turbine, power evacuation scheme and interfacing with the grid. This system requires water treatment plant, deaerator, DM water plant and condensate polishing unit, condenser and cooling tower.

Tape Calandering of Solid oxide fuel cell

Solid oxide fuel cell
A solid oxide fuel cell (SOFC) produces electricity directly from oxidizing a fuel and has a solid oxide or ceramic, electrolyte. Advantages of solid oxide fuel cells include high efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues.
Methods of fabrication
Currently, all R&D efforts are focused on fabrication methods of ceramic SOFC components.
SOFC components manufacturing processes.
Stiff structural ceramic parts can be manufactured by:
Extrusion
Dry pressing
Tape casting and
Calandering
Functional ceramic parts can be manufactured by:
Screen printing
Slurry coating
EVD, PVD and
Plasma and flame spraying
Tape Calandering
In Tape Calandering , a continuous thin sheet or tape of controlled thickness is produced. A high intensity mixer is used to mix the ceramic powder, binder and plasticiser. The mixing results in heating-up the batch and softening the binder to form a plastic mass. Then, the mass is rolled to form a thin, flat tape using a two-roll mill, and adjusting the spacing between the two mills controls the tape thickness.
This technique is used to fabricate monolithic FCs via a co-sintering process, where the individual tapes are laminated in a second rolling operation, and FCs with very thin electrolyte layer, which enables to operate at low temperatures (600 ºC) is produced.
The fabrication details of typical 2 cm2 area fuel cell components which includes preparation of anode, electrolyte, cathode cermet pastes, nickel net (60 mesh and grip on anode side) are given below.
• Anode: NiO,
• Cathode: perovskite Ca0,9La0,1MnO3 (CLM),
• Electrolyte (SDCm-1)
Cermet proportions
• Anode: Electrolyte cermet, at: 1:1, % by volume
• Cathode/electrolyte cermet, at 1:1 % by volume
• Binder : 3% Teflon by mass to every component
• Nickel net dimensions: Anode: 22x22 mm,
• Anode/Cathode thickness: 0.5 mm each, including nickel net
• Electrolyte thickness: 0.5 mm
• Sintering of samples: 600 °C, 2 h under nitrogen atmosphere