Cacia Pulp mill Portugal

Transcription

1 THE ANALYSIS REPORT OF PLANT NO. 15 Cofiring of biomass - evaluation of fuel procurement and handling in selected existing plants and exchange of information (COFIRING) - Part 2 Cacia Pulp mill Portugal Evaluated by Teresa Almeida, CBE

2 Contents Contents General information of the plant Process description Fuels and fuel procurement Fuel handling and feeding system Combustion Ash handling Control and cleaning Investment and maintenance costs Remarks and conclusions...9 2

3 1. General information of the plant PORTUCEL INDUSTRIAL, is a private enterprise producing fully bleached sulphate eucalyptus market pulp and sack kraft paper, in CACIA and SETÚBAL. This report concerns the industrial process developed in CACIA factory. At present this mill produces, in a batch line, about ADT per year of total unbleached pulp, ADT of fully bleached pulp and ADT of paper. In the factory nowadays work 490 employees, 43 of them on Cacia Energy Department. In the year 1987 it was decided the modernisation of the power plant with increased capacity and considering the main advantages of use it was installed a wood waste burning boiler - a Babcok Enterprise boiler. The former auxiliary boiler used only naphta. The choice of the boiler type was based on know-how experience at the time, easiness of operation and reliability. In normal operation, priority is given to the use of available biomass fuels, but the continuous operation of the entire mill requires 100% boiler availability leading to the use of the fossil fuel to keep the required steam flow. Steam pressure control to answer to rapid demand changes is assured by control of fuel oil flow. Electricity can either be purchased or sold to the national grid depending on local production and demand. As the plant turbine is a backpressure turbine, the grid assures frequency control. Boiler design was based on average characteristics of available fuel: eucalyptus and pine bark and sawdust, wood chips from forest management operations (cleaning, thinnings, etc.). At the time of the project, heavy fuel oil was the only suitable fuel available. Natural gas was not available and local coal was of very low quality. The use of coal was also not recommended because of possible dust contamination of mill products. The mill is equipped to comply with the most demanding environmental conditions including elemental chlorine free bleaching, high efficiency washing, gas scrubbing and high efficiency electrostatic precipitators for the recovery boilers and lime kilns, biological effluent treatment, etc. 3

4 2. Process description The mill power plant includes two black liquor recovery boilers with indirect contact evaporators and another boiler prepared to burn biomass and fuel oil. The auxiliary boiler can produce 125 t/h of steam at 64 bar burning biomass and fuel oil, and 105 t/h of steam burning only biomass. After the modernisation that occurred in 1987, the electricity is produced in a new single extraction back pressure steam turbine at 2.5 bar, with controlled extraction at 10.3 bar and it is supplied with the steam produced at the boilers. The turbo generator has a production capacity of 28.6 MW at 15kV. Another turbo generator, which did not function until 1997, was again utilised from that year on. Its capacity is 5 MW in condensation. The connection with the national net is made at a substation with an installed capacity of 10 MVA, 60/15 kv. In figure 1 we can observe a power production scheme in CACIA. Figure 1. Steam and electricity production. 4

5 3. Fuels and fuel procurement As explained before main fuels are either locally produced (eucalyptus bark, sawdust, wood chips), or purchased from others (wood chips, bark, sawdust, olive bagass and almond shells). The next figure presents a scheme about biomass treatment and combustion in CACIA. Figure 2. Biomass handling system. The fuel produced locally comes from the manufacture process. The eucalyptus wood is, in most, received as 2.20 m logs with bark. To remove the bark and to transform the logs in chips, there is an installation composed by: - Discharge table with logs ordering - Pre-treatment unit - Drum to remove bark - Station of logs wash - Chipper - Vibratory sieve of chips - Bark transporters - Bark disintegration - Bark silo 5

6 The bark is used as fuel in the biomass boiler. There is a place in the bark silo for the reception of outside acquired biomass, as well as a sieve and grinding system. Outside fuel procurement is made by contacts with sawmill operators, forest entrepreneurs, olive oil and almond producers. On the following tables some values are presented concerning biomass and fuel oil consumption for the auxiliary boiler in 1998 and 1999, as well as some characteristics of those fuels. Fuel Table 1. Fuel s consumption in cofiring boiler(1998). Annual consumption (ton) Density (kg/m 3 ) Moisture content (%) Purchased biomass Bark and Sawdust Wood chips (min 260-max 500) (min 17-max 37) 40 (min 14-max 62) Almond shells (min 6-max 30) 1998 Net calorific value (kj/kg) Olive Bagass Locally produced biomass (min 50-max 60) Fuel oil According to the preview table, in 1998 the auxiliary boiler consumed ton of biomass (68% weight) and ton of fuel oil (32% weight). Fuel Purchased biomass Table 2. Fuel s consumption in cofiring boiler (1999). Annual consumption (ton) Density (kg/m 3 ) Moisture content (%) Bark and Sawdust Wood chips (min 260-max 500) (min 17-max 37) 40 (min 14-max 62) Almond peel 0 18 (min 6-max 30) 1999 Net calorific value (kj/kg) Olive Bagass Locally produced biomass (min 50-max 60) Fuel oil

7 Looking at table 2, it is possible to conclude that, in 1999, the auxiliary boiler consumed ton of biomass (71% weight) and ton of fuel oil (29% weight). 4. Fuel handling and feeding system The fuel, locally produced and purchased from others, mostly delivered by truck or lorry, is unloaded into a bin located at one end of the main covered silo. From the bin, the wastes are conveyed to a screening installation, and oversize particles are transported to a chipper and recycled to the screen. The feeding system is composed by: Biomass store with capacity of m 3 Screen conveyor Biomass silo to feed the boiler with 18 screws and 6 feeding conducts 5. Combustion As referred before, the steam for process is produced by two black liquor recovery boilers, in parallel with one auxiliary boiler (Babcok Enterprise) burning available fossil fuel (naphta) and residues, with a maximum production of steam of 125 ton/hour at 63 bar and 425ºC, and the electricity is produced in a single extraction back pressure turbine. The auxiliary boiler has as main components: Rotative grate of 7.9 x 6.6 m., type Detroit, composed of 7 numberless rugs. Two evaporators Tubes furnace of 67.1 x 4.6 (mm) Economiser made of two banks of 144 tubes each. Superheated consisting of 2 modules. The temperature control is done by cooling the steam in the inferior evaporator. 4 fuel oil burners and respective control stations Air feeding: - 2 fans for combustion of the fuel oil (1 fan for burners north side and 1 fan for burners south side) 7

8 - 2 fans for combustion of biomass (1 fan of primary air to feed the inferior part of the grill and 1 fan of air to feed the impelling of the biomass and the admission of secondary air) For security reasons, (biomass supply can occasionally be unavailable at the required quantity), the boiler is designed to produce full load at 100% fuel oil and fuel oil plus biomass, and less than 100% load (like 80% of full load) when burning only biomass (biomass heat content is lower). The following table presents the operation conditions on the auxiliary boiler. Table 3. Cofiring boiler operation conditions. Flow of fuel kg/s Biomass Fuel Vaporisation t/h (B)-biomass fuel, (F)-fossil fuel 50(B) 55(F) 100(B) 25(F) 40(B) 85(F) Revenue Steam Temperature ºC: Primary admission superheater Primary exit superheater Primary admission superheater Primary exit superheater Water Temperature ºC: Feeding water Admission economiser Exit economiser Ash handling The ash system is composed by: Primary ashtray (fall of the grate) Secondary ashtray (inferior side of the grate) Electrostatic precipitator (flying ashes) Silo Saxlund with humidifying system with hot water, volume 290 m 3 Dust removal system 8

9 The mill is certified by ISO Control and cleaning Control of the atmospheric emissions system includes: Dust removal system Electrostatic precipitator with 3 fields series, with inferior value of 100 mg/nm 3 in particles on chimney exit. Continuous monitoring in chimneys of dust and SO 2. Limits values: Dust mg/nm 3 SO mg/nm 3 8. Investment and maintenance costs The Cacia co-generation system was built in The investment cost was approximately 29 MEuro. The company did not provide any information about maintenance costs. 9. Remarks and conclusions When the biomass boiler was installed, on 1987, it was an excellent solution with regard to the economy and availability of the plant, because it was possible to valorise the residues produced on the mill, as well as buying forest residues, almond shells and olive bagass as biomass fuels, decreasing the use of fossil fuels (naphta). During the last 13 year, some improvements were realised in order to optimise the energetic system, but nowadays some big changes are expected, and a study is being developed, concerning some technical modifications on the process, including the biomass boiler. Details are not available, at moment. 9