Biomass Boiler Testing and Selection of Suitable Biomass Fuel

In line with the trends toward decarbonization and sustainability across various sectors of life, particularly in the processing industries (manufacturing/process industries), the use of biomass boilers has become a realistic option today among boilers that utilize other renewable energy sources. Fossil-fuel-fired boilers—such as solid-fuel boilers (coal), liquid-fuel boilers (industrial diesel), and gas-fired boilers (natural gas)—must be replaced with renewable fuel boilers, namely biomass boilers. Apart from technical factors in the form of operational adjustments from previous fossil-based fuels, the suitability and availability of biomass fuels are important factors. Suitability refers to the technical aspect and availability refers to the economic aspect.

Combustion technology for biomass boilers also continues to develop so that efficiency continues to increase. From the beginning in the form of static grates to dynamic moving grates such as chain grates and reciprocating grates, even fluidized beds. And to get optimal performance, biomass fuel specifications must also match the shape, size, calorific value and dryness. If the specifications do not meet the requirements of the combustion technology in the boiler then of course the performance will not be optimal. For example, chain grates are suitable for using fuel that has a uniform size and low water content such as palm kernel shells, wood chips and wood pellets. Apart from that, biomass fuel with ash content which has a high melting point is highly preferred so that the ash does not melt and clog the chain lattice cavity.

Meanwhile, using a reciprocating grate, this system is very reliable for burning biomass with high moisture content (up to 60%), non-uniform size, and high ash content, such as empty oil palm fruit bunches (EFB), bark, and municipal solid waste (MSW). The combustion system moves back and forth periodically (like a moving staircase that moves back and forth) which functions to mechanically turn and stir the fuel. And for fluidized beds, this system has the highest thermal efficiency (>89%) and is very suitable for biomass with very small size (powder/dust), low calorific value, or fluctuating chemical content such as rice husks, sawdust, and coffee grounds. The biomass particle size must be maintained within certain limits so that it can float and fluidize perfectly with the sand bed media. The ideal particle size for a fluidized bed boiler (FBC) generally ranges from 0.1 mm to 10 mm (maximum 30–50 mm for certain components), depending on the specific type of technology used.

As a country located on the equator with a tropical climate, Indonesia is a biomass paradise in the world; read more here. A wide variety of biomass fuels in large volumes can be sourced in Indonesia. The most readily available biomass fuels in Indonesia today are wood chips, palm kernel shells, and wood pellets. Wood briquettes are also available but in limited quantities. Choosing the right biomass fuel will ensure optimal boiler performance, but of course, the economic factors for each metric ton of high-pressure steam produced are equally important. 

Ideally, biomass fuel is available in large quantities, ensuring affordability and high quality. The price of biomass fuel is influenced by various factors, including availability, location, logistics infrastructure, and transportation costs. Furthermore, if the biomass fuel undergoes processing, such as wood pellets and briquettes, production costs also contribute. Palm kernel shells for industrial boiler use in Indonesia require almost no processing; they are simply collected from palm oil mills or CPO mills, which produce waste in the form of palm kernel shells (PKS).

There is a case study regarding the selection of this biomass fuel involving a multinational company. In a certain country, the company’s boilers operate using wood briquettes—specifically, industrial briquettes produced by a mechanical press. This approach was also planned for the company’s plant in Indonesia. However, because producers of wood briquettes are still very scarce in Indonesia—making it impossible to secure a supply—the company ultimately conducted various experiments and trials with different types of biomass fuels and now operates its boilers using wood pellets. Thus, in addition to technical factors, economic factors are also crucial for ensuring optimal and sustainable biomass boiler operations. The trial phase is a critical step in achieving these conditions. 

Water Related Problems in Cooling Towers

The constant trickle of water can hollow out rocks. Furthermore, a continuous flow of water will gradually erode everything in its path. A more dramatic and spectacular example is the Grand Canyon in Arizona, United States. Furthermore, if the flowing water is hot, it will erode or dissolve the solids it passes through (leaching) more quickly than cold water. By the time the hot water returns to the cooling tower, it is already full of suspended solids. The cooling tower, as a means of dissipating heat, flows hot water from the top of the tower, and cool air from the surrounding environment that comes into contact with the warm water absorbs the heat. As a result, the water becomes cooler and the air becomes warmer.

Hot water also tends to be corrosive and form deposits. This is why the materials used to construct cooling towers must be durable and able to withstand large temperature differences. Certain types of wood and plastic can be used for cooling tower construction. If the materials are of poor quality, the cooling tower construction will be short-lived and even dangerous. When hot water enters the cooling tower and mixes with suspended solids, some of the water evaporates, leaving the suspended solids behind. This suspended solids-rich liquid concentrates in the sump at the bottom of the cooling tower. Over time, the concentration of these suspended solids increases until it reaches a level that must be controlled by removing it from the system, known as blowdown.

The outside air that comes into contact with the water from the cooling tower contains dust or small particles, as well as microorganisms such as various bacteria, fungal spores, and algae. These dust or small particles become suspended and accumulate/concentrate, forming deposits in the form of mud or crust. In the presence of sunlight, these microorganisms, such as bacteria and algae, photosynthesize, multiplying and increasing in number. Pathogenic bacteria like Legionella can even cause Legionnaires' disease. This mud and algae contaminate and clog heat exchanger tubes, accelerating their corrosion.

In the heat exchanger, if the scale thickness is 0.3 mm, it is estimated that there will be a heat/energy loss of 10% and if the scale thickness is 0.6 mm, it is estimated that there will be a heat/energy loss of 23%. And in general, fouling causes an annual energy/heat loss of around 15%, so it requires maintenance and pipe replacement every 3–5 years. If not handled properly, heat/energy loss due to fouling can reach up to 70% after five years. Fungi and bacteria will cause wood to rot/decompose, making it brittle and destroyed. Likewise, oxidation reactions on metal surfaces, because these metals release electrons or capture oxygen, causing corrosion on the metal. Corrosion on metal causes the metal to become increasingly eroded, brittle and damaged.

Maintaining water quality from various contaminants in a cooling tower, which volume thousands of tons per hour and operates 24 hours a day, is certainly not simple. Only by maintaining this water quality can the cooling tower's performance and lifespan meet its design targets. Using effective, efficient, and environmentally friendly technology is the best option. Advanced Oxidation Process (AOP) technology is an innovation to address these issues. This technological approach effectively, efficiently, and environmentally friendly addresses various water issues in cooling towers. For example, in algae cells, ions from the Advanced Oxidation Process (AOP) attack the sulfide groups contained in amino acids in the remaining proteins involved in photosynthesis. As a result, photosynthesis is inhibited, and the cells dissolve or disintegrate. If algae and microbial cells remain, their regrowth is inhibited by the AOP ions in the water, thus preventing algae growth. During this process, bacteria are also killed or rendered inactive.

The second example is the rust prevention mechanism of pipes. Iron (Fe) loses electrons according to the oxidation reaction and forms rust. However, when the AOP material participates in this reaction and releases electrons first, the iron is prevented from releasing electrons, thus suppressing rust formation. The rusted iron is converted to black rust through the AOP reaction, forming a dense oxide film that prevents further corrosion and protects the pipe and structure.

And the third example is the scale prevention mechanism. When water passes through the AOP system, calcium (Ca) and magnesium (Mg) ions—the components that cause hardness—are removed through crystallization in the liquid phase, thus softening the water. The resulting calcium carbonate particles cannot adhere to pipes. In hard water containing calcium (Ca) and magnesium (Mg) ions, needle-like scale structures typically form and adhere to pipe walls. Through AOP treatment, scale-forming ions undergo particle growth in the liquid phase, forming spherical particles ranging in size from a few micrometers to tens of micrometers.

According to the Gibbs–Kelvin formula, the volumetric free energy is reduced and the adhesive force is lost, thus preventing it from sticking to the pipe walls. Scale will accumulate at the bottom of the basin and be removed by a blowdown mechanism. In addition, this AOP technology will also remove scale that has already stuck to the pipes (scale removal existing pipes) and also the sterilization effect which is also very important for the quality of the cooling tower water such as preventing wood rot/decaying and killing pathogenic bacteria, both of these aspects will be explained on another occasion, Insha Allah.

To measure cooling tower performance based on the problems encountered and the solutions implemented, several parameters are used. These parameters include:
• Water pH
• Total dissolved solids (TDS)
• Tower equipment checklist
• Filters and strainers
• Wet bulb temperature and humidity

Meanwhile, safety in cooling towers is also important and needs to be considered. These include:
• Chemical additives (if used and not yet using AOP technology)
• Rotating equipment
• Dangers of hot water
• Working at heights
• Working safely on the cooling tower.
• Equipment failures
• Metal corrosion and wood rot/decay

The use of cooling towers can be said to be an important and fundamental equipment for industrial operations in general. Starting from power plants that still use fossil energy, cofiring or biomass power plants to geothermal power plants, data centers, chemical industries, biorefinery industries, petrochemical industries, iron and steel industries, food industries, pharmaceutical industries, textile industries, pulp and paper industries and so on. Related to the era of decarbonization and sustainability / sustainability of the use of renewable energy such as biomass including wood pellets and palm kernel shells / PKS as part of carbon neutral fuels or carbon negative such as carbon capture and storage (CCS) to biochar, of course environmentally friendly technology, especially easy to operate, affordable investment costs to repair-maintenance, will be an option for these industries, such as AOP technology for water conditioning in cooling towers so as to provide significant savings.

Optimizing Cooling Tower Performance by Improving Water Quality with Environmentally Friendly AOP Technology

Cooling towers are important and vital equipments for the operations of various processing industries at large. This cooling process is very important for the processing industry, chemical industry, oil and gas industry (oil refineries and petrochemicals), biofuel and biorefinery industries, power plants (fossil fuel and biomass), geothermal and large-scale (hyperscale) data centers. With the process conditions achieved, the industry can produce products that are economical/efficient and stable.

The cooling medium in the industry or factory is water, and the water is cooled in a cooling tower. And air from the atmosphere is used to cool warm water from industrial or factory processes through this cooling tower. This results in direct contact between air from the atmosphere and the warm water to be cooled. This is a source of pollution for the cooling tower water. A certain amount of additional water (make-up water) also needs to be added to replace lost water such as blow down, leaks and so on.

With continuous 24-hour operation for almost a whole year with a large volume of circulating cooling water, up to thousands of tonnes/hour, it is certainly not a simple matter to be able to maintain good and stable water quality. If water quality cannot be maintained, a number of serious problems will arise. A number of problems for cooling tower operations such as corrosion, scale, layers formed by green algae, organic materials and a number of micro organisms will reduce the performance of the cooling tower. If this happens, heat exchange will be disrupted and energy requirements for cooling tower operations will increase. When the cooling process does not work as it should, it will also affect product quality and the durability of production equipment, in the extreme case, if the cooling tower does not function, the industry or factory will stop operating (shut down).

If the cooling tower is damaged or has low efficiency, such as due to scale, there will be a low heat dissipation effect and a lot of energy loss. Then rust causes the pipe to become brittle and leak, resulting in a short life span for the pipe. Then the appearance of green algae, moss and mud from the accumulation of organic material, these things will disrupt the flow of water and even block pipes and valves. Another nuisance is the presence of bacteria and especially legionella (pathogenic bacteria that cause legionellosis) which causes various health problems.

Cold water as the output/product of the cooling tower will be used as a cooling medium in industry or factories such as condensers or other heat exchangers. The layer of fouling formed by scale on the surface of the heat exchanger ultimately reduces the overall heat transfer coefficient. In general, about 15% of energy is lost each year due to a decrease in heat transfer efficiency caused by fouling. Therefore, it is necessary to replace the pipes periodically every 3 to 5 years, and that is not a cheap cost. Even if the fouling problem is not controlled, heat loss can reach up to 70% after five years of operation.

If a problem occurs, repairs need to be carried out and often cooling tower repairs are expensive. A number of improvements/repairs to the cooling tower include structural repairs, replacement of mechanical components, drift eliminators, water distribution and fill types. Apart from the design problems of the cooling tower equipment manufacturers, water quality problems greatly affect the performance and lifespan of the equipment. This means that one solution is that efforts to maintain water quality must be maximized.

AOP (advanced oxidation process) technology has become the focus of developed countries to maximize water quality, including water as a cooling medium that is processed in cooling towers. AOP technology provides complete sterilization without leaving toxic residues and exhibits much stronger oxidizing power than conventional oxidants such as chlorine, chlorine dioxide and potassium permanganate. AOP technology specifically designed for reaction speed and intensity will be very effective for this purpose.

Compared to chemical treatment, although chemical treatment is still commonly used, there are restrictions due to environmental pollution and formaldehyde production, as well as because workers are exposed to serious dangers. As the restrictions on environmental pollution by respective governments become increasingly stringent, the use of chemicals will become increasingly restricted. Several developed countries are starting to control the addition of chemicals. The Singapore government has banned the addition of chemicals to cooling towers since 2008.

If you are interested in knowing AOP technology and its application for cooling tower water conditioners, please contact: eko.sbs@gmail.com