sludge biomass incenerator

SLUDGE BIOMASS INCINERATOR

I. Introduction

Biomass has always been used as a localized energy source. Its seasonal availability, low calofiric value, and density make it less attractive as a fuel in centralized power generation system mainly because of higher costs associated with its storage and transportation. Not withstanding these constrains biomass fuel can be used together with coal in existing combustion system.
The use of biomass as a new energy is being promoted to prevent global warming by reducing greenhouse effect gases and to use waste more effectively for the realization of a recycling-oriented society. To use the energy from biomass resource, energy producers must find mechanism that meet the needs of business entities for achieving stable supply, economic efficiency, and adequate control of fluctuating fuel properties during the processes of biomass collection, energy conversion and the use of the biomass resources.
Paper Sludge as a fuel
Through photosythesis, the energy stored in biomass is theoretically almost 10 times of the world energy consumption. The option to use paper sludge as a bio-waste fuel for energy production has been recently considered in many European countries. The organic fraction in paper sludge is renewable, and therefore it does not contribute to net CO2 emissions. A few mills incinerate paper sludge in their boilers as “hog” fuel. This practice is not widespread, because the heating value is very low and the high moisture of the sludge affects its ability to burn efficiently. To enhance the heating value, the sludge is mixed with dryer waste materials (such as wood residue). Fluidized bed combustion is an emerging technology that works particularly well with the wet sludge produced by de-inking mills. In this process, air is bubbled through a bed of inert material (usually sand or limestone), which greatly improves the combustion process. This technology also produces fewer sulfur dioxide and nitrous oxide emissions than do conventional hog boilers. Burning sludge is advantageous because the landfill volume required for ash disposal is about 25 percent of that required for sludge. In addition, boiler ash from de-inking sludge incineration is sometimes used as an aggregate in cement and concrete.
Sludge ash concentrates heavy metals, however, and if their concentration arises hazardous levels, the ash requires special handling, (Shin et al., 2005; Usherson, 1992). Every tone of recovered fiber generates up to 200 kg (dry weight) of sludge of different types and up to 400 kg (dry weight) of rejects and sludge, the amount of rejects and sludge depending on the recovered paper grades and paper produced (Scott et al., 1995).
De-inking sludge consist of printing inks (black and colored pigments), fillers and coating pigments, fibers, fiber fines, and adhesive components. More than 55 % of the solids removed by flotation are inorganic compounds. They are primarily fillers and coating pigments such as clay and calcium carbonate. The proportion of cellulosic fiber is low. The heating value depends on the ash content and is 4.7–8.6 GJ/t of dry substance, (Hamm, 2006). The sulfur, fluorine, chlorine, bromine, and iodine contents are low and for this reason, no costly flue gas purification systems are necessary when incinerating de-inking sludge. Compared with sludge from biological effluent treatment plants, the nitrogen and phosphorus contents are very low. This is something that requires consideration when using de- inking sludge for composting and agricultural and land application purposes. The level of heavy metals in sludge of recovered paper processing is generally low. Sludge of de-inking plants contains less contamination than those of municipal wastewater treatment. The concentration of cadmium and mercury is especially insignificant and sometimes even below the detection limit of the test method applied (atomic absorption spectrometry). Only the concentration of copper has the same order of magnitude as that of municipal sewage sludge. The copper content of de-inking sludge is primarily due to blue pigments of printing inks which contain phthalocyano- compounds (Kiphann, 2001).

Greenhouse gas emissions
The Kyoto Protocol set very ambitious targets for reducing energy consumption and emission of greenhouse gases (GHG). Emissions included in the inventory were as follows:
- carbon dioxide emission from fossil fuel combustion that includes those from production processes, as well as from the use of company owned vehicles and from other equipments producing CO2. Emissions are estimated using widely-accepted emission factors, which are based on the carbon content of the fuel;

- methane and nitrous oxide emissions from combustion processes, which are estimated using emission factors. Emissions of CH4 dan N2O are usually very small compared to those of CO2 and some inventory protocols do not address such emissions;

- greenhouse gas emissions from mill landfills and wastes water treatment plants, which are estimated using mill-generated data, and are consistent with methods suggested by the Intergovernmental Panel on Climate Change (IPCC).

This problem can be solved by technology of carbonization system to recycle sludge for electric power generation fuel. The technology can satisfy two needs at the same time:
1. The need to recycle sludge and supress the emission of Global Warming gases in sludge treatment plants;
2. The need to substitute fuel with carbon free fossil fuel in thermal power plants.





II. Coal and Biomass Fuel

The whole process of coal formation (coalification) was an unremitting geochemical evolution, starting with the decay of organic materials in swamps and followed by their metamorphosis under the in u- ence of geological forces (depth of sinking, temper- ature, and tectonic shear forces). A detailed account of coalification is well beyond the scope of this re- view.
Biomass fuels may be defined as combustible materials resulting from silviculture, agriculture, and aquaculture, that is, fuels resulting from the growing of plants and the raising of animals. These fuels are also distinguished by the fact that biomass generally exists in a diffuse state and must be gathered up and concentrated in a single location for use, rather than being produced in a single location (i.e., a coal mine) and dispersed for use. Some specific biomass varieties being considered as useful fuels include wood and wood wastes (e.g., hogged bark and sawdust), spent pulping liquor, rice hulls, cotton gin trash, ba- gasse, coffee grounds, wood waste from wood struc- tures, manure, sewage sludge, and myriad other biomass forms. We emphasize pulverized dried sewage in this paper because of its similar combustion behavior to that of lignite coals, as well as its biological origin.
Through photosynthesis, the energy stored in biomass is theoretically almost 10 times that of the world energy consumption. Currently, biomass supplies approximately 14% of humanity’s total energy requirement. Much of this is inefficiently consumed by poorer people in developing countries where the practice frequently results in the long-term loss of vegetation. In the European Union (EU), “renewables” contribute to some 2% of its energy require ment, roughly half of which is attributed to biomass combustion. The EU plans a twofold increase by, 2005, mainly from the deployment of energy crops grown on land that is either deforested, degraded, or set aside from crop production.

There are several routes for upgrading biomass (conversion to gaseous or liquid fuels), all with dis advantages. Within the context of this paper, we should mention the producing of “biocoal” in which the biomass is coalified through low-temperature processes in which the oxygen-rich biomass precursors are transformed to cross-linked aromatic and hydrogen-rich mattes. Pressurized or confined py rolysis allows one to follow the natural trends of organic matter maturation, to generate an artificially matured series of coals from biomass, and to observ the evolution of hydrocarbon production throughout the maturation process. This has been achieved in a bench-top cold-seal autoclave in which a few hundred grams of each maceral and raw biomass have been pyrolysed under isothermal conditions in sealed gold tubes at temperatures ranging between 150 and 500 C for more than 24 h at a constant pressure of 100 Mpa. On the commercial scale, however, the process is unlikely to be energy efficient.


III. Energy from Biomass in Pulp and Paper Mills

IV. Process and Equipment of Sludge Biomass Incinerator in Pulp and Paper Mills
a. Sludge Dewatering
b. Drier
c. Incinerator (PFBC)
d. Heat Recovery Steam Generator
e. Heat and Electricity
f. Flue Gas Cleaning
V. Conclusion