Contractors

Carbonization

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Carbonization is the complex process of concentrating and purifying carbon by denaturing organic matter with heat in the presence of little to no oxygen.

Carbonization is a pyrolytic reaction, therefore, is considered a complex process in which many reactions take place concurrently such as dehydrogenation, condensation, hydrogen transfer and isomerization.

Carbonization differs from coalification in that it occurs much faster, due to its reaction rate being faster by many orders of magnitude.

For the final pyrolysis temperature, the amount of heat applied controls the degree of carbonization and the residual content of foreign elements. For example, at T ~ 1200 K the carbon content of the residue exceeds a mass fraction of 90 wt.%, whereas at T ~ 1600 K more than 99 wt.% carbon is found. Carbonization is often exothermic, which means that it could in principle be made self-sustaining and be used as a source of energy that does not produce carbon dioxide.

The carbonization of wood in an industrial setting usually requires a temperature above 280 °C, which frees up energy and hence this reaction is said to be exothermic. This carbonization, which can also be seen as a spontaneous breakdown of the wood, continues until only the carbonised residue called charcoal remains. Unless further external heat is provided, the process stops and the temperature reaches a maximum of about 400 °C. This charcoal, however, will still contain appreciable amounts of tar residue, together with the ash of the original wood.

The gas produced by carbonization has a high content of carbon monoxide which is poisonous when breathed. Therefore, when working around the kiln or pit during operation and when the kiln is opened for unloading, care must be taken that proper ventilation is provided to allow the carbon monoxide, which is also produced during unloading through spontaneous ignition of the hot fuel, to be dispersed.

The tars and smoke produced from carbonization, although not directly poisonous, may have long-term damaging effects on the respiratory system. Housing areas should, where possible, be located so that prevailing winds carry smoke from charcoal operations away from them and batteries of kilns should not be located in close proximity to housing areas.

Wood tars and pyroligneous acid can be irritant to skin and care should be taken to avoid prolonged skin contact by providing protective clothing and adopting working procedures which minimize exposure.

The tars and pyroligneous liquors can also seriously contaminate streams and affect drinking water supplies for humans and animals. Fish may also be adversely affected. Liquid effluents and waste water from medium and large scale charcoal operations should be trapped in large settling ponds and allowed to evaporate so that this water does not pass into the local drainage system and contaminate streams. Kilns and pits, as distinct from retorts and other sophisticated systems, do not normally produce liquid effluent – the by-products are mostly dispersed into the air as vapours.

Coating

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A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. Powder coatings.

Paints and lacquers are coatings that mostly have dual uses of protecting the substrate and being decorative, although some artists paints are only for decoration, and the paint on large industrial pipes is for preventing corrosion and identification e.g. blue for process water, red for fire-fighting control etc. Functional coatings may be applied to change the surface properties of the substrate, such as adhesion, wettability, corrosion resistance, or wear resistance. In other cases, e.g. semiconductor device fabrication (where the substrate is a wafer), the coating adds a completely new property, such as a magnetic response or electrical conductivity, and forms an essential part of the finished product.

A major consideration for most coating processes is that the coating is to be applied at a controlled thickness, and a number of different processes are in use to achieve this control, ranging from a simple brush for painting a wall, to some very expensive machinery applying coatings in the electronics industry. A further consideration for ‘non-all-over’ coatings is that control is needed as to where the coating is to be applied. A number of these non-all-over coating processes are printing processes. Many industrial coating processes involve the application of a thin film of functional material to a substrate, such as paper, fabric, film, foil, or sheet stock. If the substrate starts and ends the process wound up in a roll, the process may be termed “roll-to-roll” or “web-based” coating.

Coatings are not just designed to be aesthetically pleasing and for decorative purposes, but also have other functions. Sometimes a coating can be both decorative and have a specific function. An example would be the coating of a pipe carrying water for a fire suppression system that is coated with a red (for identification) anticorrosion paint to reduce degradation. In fact, most surface coatings or paints are to some extent protecting the substrate e.g. general maintenance coatings/paints for metals and concrete. The decorative aspect of coatings is not just to impart a specific color, but also to create a particular reflective property such as high gloss, satin or flat/matt appearance. Some coatings though, are specifically designed to be very chemically resistant.

A major use of coatings is to protect metal, and these are generally known as anticorrosion coatings. This use includes preserving machinery, equipment and structures. Automobiles have improved in design over the years. Most are still made of metal for crashworthiness. The external coating and the underbody are coated.

Coatings are also used to seal the surface of concrete. This would include Seamless polymer/resin flooring, bund wall/containment lining, Waterproofing and damp proofing of concrete walls, and concrete bridge decks.

Roof coatings have been developed and improved over the years. They are designed primarily for waterproofing and also sun reflection to help keep a building cool. They tend to be elastomeric to allow for movement of the roof without cracking the coating membrane.

The coating, sealing and waterproofing of wood has been going on since biblical times, with God commanding Noah to build an ark and then coat it. Wood was and is a key material of construction since ancient times so its preservation by coating has received much attention. Efforts to improve the performance of wood coatings continues.

Coatings are used to alter tribological properties and wear characteristics. Other functions of coatings include :

  • UV coatings
  • Anti-reflective coatings for example on spectacles.
  • Non-stick PTFE coated cooking pots/pans.
  • Optical coatings are available that alter optical properties of a material or object.
  • Anti-Friction, Wear and Scuffing Resistance Coatings for Rolling-element bearings
  • Coatings that alter or have magnetic, electrical or electronic properties.
  • Antimicrobial coatings.
  • Anti-fouling coatings
  • Flame retardant coatings.

Coating analysis and characterization

Numerous destructive and non-destructive evaluation (NDE) methods exist for characterizing coatings. The most common destructive method is microscopy of a mounted cross-section of the coating and its substrate. The most common non-destructive techniques include ultrasonic thickness measurement, X-ray fluorescence (XRF), X-Ray diffraction (XRD) and micro hardness indentation. X-ray photoelectron spectroscopy (XPS) is also a classical characterization method to investigate the chemical composition of the nanometer thick surface layer of a material. Scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDX, or SEM-EDS) allows to visualize the surface texture and to probe its elementary chemical composition. Other characterization methods include transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscope (STM), and Rutherford backscattering spectrometry (RBS). Various methods of Chromatography are also used, as well as thermogravimetric analysis.

Thermal Cleaning

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Pyrolysis is also used for thermal cleaning, an industrial application to remove organic substances such as polymers, plastics and coatings from parts, products or production components like extruder screws, spinnerets and static mixers. During the thermal cleaning process, at temperatures between 310 C° to 540 C° (600 °F to 1000 °F), organic material is converted by pyrolysis and oxidation into volatile organic compounds, hydrocarbons and carbonized gas. Inorganic elements remain.

Several types of thermal cleaning systems use pyrolysis:

  • Molten Salt Baths belong to the oldest thermal cleaning systems; cleaning with a molten salt bath is very fast but implies the risk of dangerous splatters, or other potential hazards connected with the use of salt baths, like explosions or highly toxic hydrogen cyanide gas.
  • Fluidized Bed Systems use sand or aluminium oxide as heating medium; these systems also clean very fast but the medium does not melt or boil, nor emit any vapors or odors; the cleaning process takes one to two hours.
  • Vacuum Ovens use pyrolysis in a vacuum avoiding uncontrolled combustion inside the cleaning chamber; the cleaning process takes 8 to 30 hours.
  • Burn-Off Ovens, also known as Heat-Cleaning Ovens, are gas-fired and used in the painting, coatings, electric motors and plastics industries for removing organics from heavy and large metal parts.

Ethylene and Semiconductors

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Ethylene

Pyrolysis is used to produce ethylene, the chemical compound produced on the largest scale industrially (>110 million tons/year in 2005). In this process, hydrocarbons from petroleum are heated to around 600 °C (1,112 °F) in the presence of steam; this is called steam cracking. The resulting ethylene is used to make antifreeze (ethylene glycol), PVC (via vinyl chloride), and many other polymers, such as polyethylene and polystyrene.

Semiconductors

The process of metalorganic vapour-phase epitaxy (MOCVD) entails pyrolysis of volatile organometallic compounds to give semiconductors, hard coatings, and other applicable materials. The reactions entail thermal degradation of precursors, with deposition of the inorganic component and release of the hydrocarbons as gaseous waste. Since it is an atom-by-atom deposition, these atoms organize themselves into crystals to form the bulk semiconductor. Silicon chips are produced by the pyrolysis of silane:

SiH4 → Si + 2 H2.

Gallium arsenide, another semiconductor, forms upon co-pyrolysis of trimethylgallium and arsine.

Methane Pyrolysis for Hydrogen

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Methane pyrolysis is a industrial process for “turquoise” hydrogen production from methane by removing solid carbon from natural gas. This one-step process produces hydrogen in high volume at low cost (less than steam reforming with carbon sequestration). Only water is released when hydrogen is used as the fuel for fuel-cell electric heavy truck transportation, gas turbine electric power generation, and hydrogen for industrial processes including producing ammonia fertilizer and cement.

Methane pyrolysis is the process operating around 1065 °C for producing hydrogen from natural gas that allows removal of carbon easily (solid carbon is a byproduct of the process). The industrial quality solid carbon can then be sold or landfilled and is not released into the atmosphere, avoiding emission of greenhouse gas (GHG) or ground water pollution from a landfill. Power for process heat consumed is only one seventh of the power consumed in the water electrolysis method for producing hydrogen.

Chemical Waste Gases Treatment

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With chemical absorption, an ion, atom or molecule is absorbed into the free volume of the absorbing phase. The process of gas scrubbing is used, among other things, for the treatment of industrial waste gases or for the removal of odours. As an absorbent, water is used and – depending on the pollutant – the addition of specific chemicals (chemisorption) takes place. In most cases, very high treatment performance is achieved.

To achieve the required treatment performance at low operating costs. We designs and manufactures various kinds of scrubbing types for different applications such as

  • Counter-flow scrubber
  • Cross-flow scrubber
  • Direct-flow scrubber

They can be installed in one or more stages or can be used as emergency units.

In addition to scrubbers, We offers activated carbon filters for the adsorption of air pollutants. Activated carbon is fine-grained carbon with a highly porous structure and a very large surface. By attachment on the inner surface of the activated carbon, harmful or odorous substances are removed from gases, vapours and liquids.

In activated carbon filters, They can be used to eliminate a wide range of harmful or odorous substances such as

  • Hydrogen sulphide
  • Indole and skatole
  • Methylmercaptane
  • Methylamines
  • Ammonia
  • VOC

Waste Gas Treatment — Pyrolysis

The process waste gases are burnt in a decomposition zone. If required, a fuel gas can be applied. Depending on the chemical composition of the waste gases, various reactions take place, such as oxidation, reduction or pyrolysis.

 

 

 

Wet Scrubber Treating Water-Soluble Substances

Wet scrubbing is an efficient process for the treatment of water-soluble pollutants in process exhaust gases. Our wet scrubbers are employed mainly in the semiconductor industry wet treatment system. Installed closely behind the vacuum pumps, they optimally protect the fab’s exhaust gas system from contamination and corrosion. Maintenance is quick and easy.

Biologycal Waste Gases Treatment

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In biofilters, harmful and odorous substances from waste-gas and exhaust-gas flows are decomposed to non-toxic, odourless and largely low molecular weight substances, such as carbon dioxide and water. This is done biochemically by the metabolic activity of microorganisms. For this purpose, the pollutant to be separated is first dissolved and microbiologically degraded.

It must be ensured that the metabolic activity of the microorganisms used can proceed at an optimum level. It is often useful here to use other substances such as, for example, phosphorus or trace elements.

We offers appropriate system types and construction tailored to the application

  • Bio scrubbers, biofilters, biotrickling filters/ trickle bed reactors
  • Single-stage or multi-stage – for example with upstream bio- or chemo-scrubbers
  • Surface, circular and floor filters
  • Container plants as well as compact and mobile biofilter plants
  • Closed biofilter for targeted waste-gas flow guidance

In biofilters, microorganisms are settled on an organic substrate (e.g. bark or woodchips). In addition to the pollutants, this serves the organisms as a nutrient substrate. For pollutant removal, the waste gas is blown into the filter bed from the bottom to the top. With their simple design, biofilters can be operated cost-effectively in applications with low pollutant loading.

In contrast to biofilters, the microorganisms used are suspended in the scrubbing liquid in bio scrubbers. The pollutants are extracted from the waste gas and then biodegraded. Depending on the pollutant load, the decomposition occurs in the absorber sump or in an additional external regeneration reactor.

In biotrickling filters, inert substrates are used instead of the biological substrates in conventional biofilter methods, on which the microorganisms are settled. Organic and inorganic gaseous compounds are biochemically oxidised under aerobic conditions and converted into low molecular weight, non-harmful compounds which are no longer perceptible, such as carbon dioxide and water. The laden waste gas flows through the substrate in cross, counter and direct flow with respect to the trickling liquid.

Electrostatic Collection of Micro and Nanoparticles

Electrostatic filters use an electric field to clean process waste gases from particles. Our systems filter micro and nanoparticle-containing or aerosol-containing process waste gases as they occur.

For the treatment of condensable organic compounds, we offer an electrostatic condensate separator.

Landfill Gas

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Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Trace amounts of other volatile organic compounds (VOCs) comprise the remainder (<1%). These trace gases include a large array of species, mainly simple hydrocarbons.

Landfill gases have an influence on climate change. The major components are CO2 and methane, both of which are greenhouse gasses. Methane in the atmosphere is a far more potent greenhouse gas, with each molecule having twenty-five times the effect of a molecule of carbon dioxide. Methane itself however accounts for less composition of the atmosphere than does carbon dioxide. Landfills are the third-largest source of methane in the US.

Because of the significant negative effects of these gases, regulatory regimes have been set up to monitor landfill gas, reduce the amount of biodegradable content in municipal waste, and to create landfill gas utilization strategies, which include gas flaring or capture for electricity generation.

Food Waste

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Food loss and waste is food that is not eaten. The causes of food waste or loss are numerous and occur throughout the food system, during production, processing, distribution, retail and food service sales, and consumption. Overall, about one-third of the world’s food is thrown away. Metaanalysis that did not include food lost during production, by the United Nations Environment Programme found that food waste was a challenge in all countries at all levels of economic development. The analysis estimated that global food waste was 931 million tonnes of food waste (about 121 kg per capita) across three sectors: 61 per cent from households, 26 per cent from food service and 13 per cent from retail.

Food loss and waste is a major part of the impact of agriculture on climate change (it amounts to 3.3 billion tons of CO2 e emissions annually) and other environmental issues, such as land use, water use and loss of biodiversity. Prevention of food waste is the highest priority, and when prevention is not possible, the food waste hierachy ranks the food waste treatment options from preferred to least preferred based on their negative environmental impacts. Reuse pathways of surplus food intended for human consumption, such as food donation, is the next best strategy after prevention, followed by animal feed, recycling of nutrients and energy followed by the least preferred option, landfill, which is a major source of the greenhouse gas methane. Other considerations include unreclaimed phosphorus in food waste leading to further phosphate mining. Moreover, reducing food waste in all parts of the food system is an important part of reducing the environmental impact of agriculture, by reducing the total amount of water, land, and other resources used.

 

Sewage Treatment

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Primary treatment

Primary treatment removes material that will either float or readily settle out by gravity. It includes the physical processes of screening, comminution, grit removal, and sedimentation. Screens are made of long, closely spaced, narrow metal bars. They block floating debris such as wood, rags, and other bulky objects that could clog pipes or pumps. In modern plants the screens are cleaned mechanically, and the material is promptly disposed of by burial on the plant grounds. A comminutor may be used to grind and shred debris that passes through the screens. The shredded material is removed later by sedimentation or flotation processes.

Grit chambers are long narrow tanks that are designed to slow down the flow so that solids such as sand, coffee grounds, and eggshells will settle out of the water. Grit causes excessive wear and tear on pumps and other plant equipment. Its removal is particularly important in cities with combined sewer systems, which carry a good deal of silt, sand, and gravel that wash off streets or land during a storm.

Suspended solids that pass through screens and grit chambers are removed from the sewage in sedimentation tanks. These tanks, also called primary clarifiers, provide about two hours of detention time for gravity settling to take place. As the sewage flows through them slowly, the solids gradually sink to the bottom. The settled solids—known as raw or primary sludge are moved along the tank bottom by mechanical scrapers. Sludge is collected in a hopper, where it is pumped out for removal. Mechanical surface-skimming devices remove grease and other floating materials.

Secondary treatment

Secondary treatment removes the soluble organic matter that escapes primary treatment. It also removes more of the suspended solids. Removal is usually accomplished by biological processes in which microbes consume the organic impurities as food, converting them into carbon dioxide, water, and energy for their own growth and reproduction. The sewage treatment plant provides a suitable environment, albeit of steel and concrete, for this natural biological process. Removal of soluble organic matter at the treatment plant helps to protect the dissolved oxygen balance of a receiving stream, river, or lake.

There are three basic biological treatment methods: the trickling filter, the activated sludge process, and the oxidation pond. A fourth, less common method is the rotating biological contacter.

Trickling filter

A trickling filter is simply a tank filled with a deep bed of stones. Settled sewage is sprayed continuously over the top of the stones and trickles to the bottom, where it is collected for further treatment. As the wastewater trickles down, bacteria gather and multiply on the stones. The steady flow of sewage over these growths allows the microbes to absorb the dissolved organics, thus lowering the biochemical oxygen demand (BOD) of the sewage. Air circulating upward through the spaces among the stones provides sufficient oxygen for the metabolic processes.

Settling tanks, called secondary clarifiers, follow the trickling filters. These clarifiers remove microbes that are washed off the rocks by the flow of wastewater. Two or more trickling filters may be connected in series, and sewage can be recirculated in order to increase treatment efficiencies.

Activated sludge

The activated sludge treatment system consists of an aeration tank followed by a secondary clarifier. Settled sewage, mixed with fresh sludge that is recirculated from the secondary clarifier, is introduced into the aeration tank. Compressed air is then injected into the mixture through porous diffusers located at the bottom of the tank. As it bubbles to the surface, the diffused air provides oxygen and a rapid mixing action. Air can also be added by the churning action of mechanical propeller-like mixers located at the tank surface.

Under such oxygenated conditions, microorganisms thrive, forming an active, healthy suspension of biological solids—mostly bacteria—called activated sludge. About six hours of detention is provided in the aeration tank. This gives the microbes enough time to absorb dissolved organics from the sewage, reducing the BOD. The mixture then flows from the aeration tank into the secondary clarifier, where activated sludge settles out by gravity. Clear water is skimmed from the surface of the clarifier, disinfected, and discharged as secondary effluent. The sludge is pumped out from a hopper at the bottom of the tank. About 30 percent of the sludge is recirculated back into the aeration tank, where it is mixed with the primary effluent. This recirculation is a key feature of the activated sludge process. The recycled microbes are well acclimated to the sewage environment and readily metabolize the organic materials in the primary effluent. The remaining 70 percent of the secondary sludge must be treated and disposed of in an acceptable manner (see Sludge treatment and disposal).

Variations of the activated sludge process include extended aeration, contact stabilization, and high-purity oxygen aeration. Extended aeration and contact stabilization systems omit the primary settling step. They are efficient for treating small sewage flows from motels, schools, and other relatively isolated wastewater sources. Both of these treatments are usually provided in prefabricated steel tanks called package plants. Oxygen aeration systems mix pure oxygen with activated sludge. A richer concentration of oxygen allows the aeration time to be shortened from six to two hours, reducing the required tank volume.

Oxidation pond

Oxidation ponds, also called lagoons or stabilization ponds, are large, shallow ponds designed to treat wastewater through the interaction of sunlight, bacteria, and algae. Algae grow using energy from the sun and carbon dioxide and inorganic compounds released by bacteria in water. During the process of photosynthesis, the algae release oxygen needed by aerobic bacteria. Mechanical aerators are sometimes installed to supply yet more oxygen, thereby reducing the required size of the pond. Sludge deposits in the pond must eventually be removed by dredging. Algae remaining in the pond effluent can be removed by filtration or by a combination of chemical treatment and settling.

Effluent polishing

For the removal of additional suspended solids and BOD from secondary effluent, effluent polishing is an effective treatment. It is most often accomplished using granular media filters, much like the filters used to purify drinking water. Polishing filters are usually built as prefabricated units, with tanks placed directly above the filters for storing backwash water. Effluent polishing of wastewater may also be achieved using microstrainers of the type used in treating municipal water supplies.