Process Overview
Pulp mill design will be very similar to designs adopted in the kraft pulp mills recently constructed or under development by leading companies in the sector, including the Fray Bentos mill in Uruguay, the Veracel Celulose mill (a Stora Enso joint venture) in Brazil (both operating mills) and the Montes del Plata Stora Enso joint venture currently under construction in Uruguay. Both the Fray Bentos mill and Veracel publish environmental data which demonstrates performance that would meet IFC requirements, and performance of at least these standards is expected from this mill.
The main technical design features that have been adopted for this P & B Mill follow Best Available Techniques (BAT) for the Pulp and Paper Industry as defined by the European Union’s Integrated Pollution Prevention and Control (IPPC) Reference Document on BAT in the Pulp and Paper Industry (“the IPPC BREF”). These and other features that reduce environmental impacts of processing operations will be described in the sections that follow.
As noted earlier in this review summary, mill construction will be in two phases. Phase I will include the CTMP and Board mills, with essential utilities, while Phase II will add the Kraft mill recovery boiler and additional utility systems. The resource efficiency and pollution mitigation measures described in the sections that follow refer to the completion of Phase II. During Phase I operation, pollutant mass flows will be reduced, and Stora Enso fully expects to meet all local regulatory requirement and applicable World Bank Group EHS Guideline emissions values.
Resource Efficiency
Process and utility systems design and controls are expected to minimize consumption of wood, energy and water.
Specific consumption of heat, power and water for the pulping processes and board machine are below or in the lower range of BAT as defined in the IPPC BREF.
Heat and power for the project will be supplied by a co-generation based utility system. In Phase I, high pressure superheated steam will be generated by a Power Boiler which will burn biomass (rejected wood, bark, primary and tertiary waste water treatment plant sludge and fiber rejects) arising from production processes and coal. During Phase I, the project will have generation capacity of approximately 50 MW of electricity and will typically import around 30 MW from the grid. In Phase II, a Recovery Boiler, fueled by black liquor, but also burning non-condensable gases will be added and power generation capacity expanded. Under design conditions at the conclusion of Phase II, coal would provide around 30% of the energy supplied to the utility system with the remainder derived from the renewable sources described. Coal is expected to provide around 20% of energy supplied during normal operating conditions.
The power boiler will adopt circulating fluidized bed technology. Overall efficiency of the cogeneration system (expressed as heat and electr
ical energy used in processes divided by the heat content of all fuels used in all boilers) is expected to be 82% in normal operations.
Greenhouse Gases
The mill will use heavy fuel oil in the lime kiln and as support fuels in the power and recovery boilers, while light fuel oil will be used in the auxiliary boiler, as start-up fuel for the power boiler and as a back-up support fuel for destruction of non-condensable gases. Coal will be the main fuel used in the power boiler.
Stora Enso did consider alternatives to coal for the power boiler. Gaseous fuels (LNG or LPG) are not available in southern Guangxi in sufficient volume for the project. Use of heavy fuel oil was ruled out because of regulatory limitations of use of oil for power generation and cost. Biomass options are also limited. Eucalyptus bark will be removed from logs at the harvesting sites and used for soil protection and improvement in the plantations, in accordance with best practice. Land acquisition for wood production has been challenging, and Stora Enso’s review did not identify competitive sources of biomass fuel for the mill.
Stora Enso has estimated greenhouse gas emissions arising from use of all fuels in the P&B mill at the completion of Phase II at around 450,000 tonnes per annum carbon dioxide equivalent. (tpa CO2 eq), of which coal contributes approximately 350,000 tpa CO2 eq. The heat content of steam produced by the recovery boiler and from process heat recovery exceeds process needs by around 20%: combustion of coal in the power boiler is needed to generate the additional steam needed in the mill’s power generation turbines. If instead of generating its own electricity the mill were to import electricity from the Chinese grid, then IFC estimates that associated Scope 2 emissions would be approximately double the 350,000 tpa CO2 eq incremental GHG footprint associated with the mill’s electricity generation.
IFC estimates that improved silviculture of the plantation assets will result in net sequestration in the order of 200,000 tpa CO2 eq. These estimates include only activities and sequestration and emission associated with plantation rehabilitation and include wood removals as an “off-project” loss.
The Company will work with IFC in its annual accounting and reporting of the Project’s GHG footprint.
Water Consumption
Water supply for the entire Tieshangang industrial area, including the P&B Mill will be taken from the Hepu reservoir system, and after 2015 will be supplemented by abstraction from the Nanliu river. This issue is described in the EIA and in the 2007 study “Water Resources Assessment Report for Tieshangang Industry Park.” This report concluded that the water demand of the entire industry area would be 230,000 m3/day by 2010, increasing to 447,000 m3/day by 2020. These estimates include 220,000 m3/day for the pulp and board mill, whereas Stora Enso expects mill water consumption to average 81,500 m3/day with a daily ma
ximum demand of 105,000 m3 for Phases I and II of the P&B mill.
Most of the area available for forestry in Guangxi is located on side slopes and hilltops which have been in forestry for at least 30-40 years. However, some recent survey data indicate a growing perception that plantations may have impacts on surface water availability. Preliminary evidence indicates that mature eucalypts do intercept and transpire more precipitation than pines or natural forests. This effect may reduce peak surface water flow rates during the rainy season and extend shallow aquifer recharge during the dry seasons in Guangxi. These effects could be more pronounced during droughts or abnormally high rainfall years. The exact impacts on surface water availability of the forest management cycle are inconclusive. As described in the ESAP, the forestry JVs will establish a long-term strategy for assessing potential impacts of plantations to surface water, continue the own surface water monitoring trials, study results from comparable trials elsewhere and will update work instructions for plantation management as necessary.
Pollution Prevention
Plantation Operations
Construction of roads, harvesting of forests, and replanting activities are a significant source of erosion which can result in sediment discharge to surface water. Limitations of road grades and use of contour planting are specified in the BMS and IOSP requirements. The use of low quantities of fertilizers, which can lead to localized pollution, in plantation establishment, is also prescribed and supervised at the site level. While overall attention to water quality concerns was observed, several cases of contractor non-compliance were noted. As described in the ESAP, the forestry JVs will ensure ongoing soil loss and soil fertility management monitoring and will adapt operating principles accordingly. Recent public surveys conducted by SEGX have identified concerns over localized water pollution.
Mill – Effluents
The P&B Mill has many design features that correspond to BAT as defined by the IPPC BREF and that reduce water consumption and effluent contamination at source. These include:
Dry debarking,
Modified cooking concept and two stage oxygen delignification
Counter current brown stock pulp washing
Closed cycle pressure screening of brown stock pulp
ECF bleaching, using a type R8 chlorine dioxide generation which has very low residual chlorine concentration in the bleach solution
Partial countercurrent washing in bleach plant for reduced water consumption
Reuse of drying machine white water in bleach plant washing
Stripping and reuse of evaporator condensates
Use of clean condensates for washing of brownstock pulp and also lime mud washing
Sufficient storage volume in brown stock washing and black liquor handling systems to manage variations in operational conditions and avoid overflow to drain.
Spill recovery system in the brown stock line, evaporation area and c
austizising area.
Collection and reuse of cooling water and clean sealing waters
Optimized white water system recirculation of the board machine, effluent <15m3/t of board.
Separation of drainage areas and sewer system in the mill according to potential for contamination of storm waters, from process areas, potentially contaminated to storm water basin and clean waters.
Emergency basin in the effluent treatment plant to manage accidental spills.
In addition to these process design features, the mill will feature primary, secondary and also tertiary treatment of liquid effluents. Tertiary treatment, which is considered beyond BAT is required in order to meet the local regulatory requirement that the concentration of COD in liquid effluents is less than 90 milligrams per litre (mg/l) for the integrated pulp and board mill.
Wash filtrates from the BCTMP process will be treated by evaporation followed by burning in a CTMP recovery boiler and including recausticizing of the sodium carbonate to sodium hydroxide for reuse in the CTMP process. Evaporation condensates will be used for pulp washing. This technology is installed at other mills producing CTMP in China and should ensure that the limit of 90 mg/l of COD is reached for the treated effluents.
The comparison in Table 2 shows that the quality of treated effluent from the kraft pulp production will be better than standards considered BAT and will more than satisfy World Bank Group (WBG) EHS Guideline values for the parameters shown.
References refer to production of bleached kraft pulp.
Dioxin emissions in effluent are regulated by the Chinese standard GB3544-2008 at <30 pg TEQ/l before effluent treatment. The mill EIA states that dioxin content of treated effluents will be <6.2 pg TEQ/l, but actual levels are expected to be comparable with other modern mills, such as the Fray Bentos and Veracel mills that both report <1 pgTEQ/l.
The effect of the mill’s routine effluent discharge, as well as a much more extreme case assuming complete failure of effluent treatment systems, on receiving water quality was analysed in the mill’s 2008 EIA. The most comprehensive modeling was of COD, which baseline studies showed was around 1.5 mg/l. The EIA concluded that while the most extreme case would elevate COD by 2 mg/l over a wide area, impacts of an accidental release would not be experienced in sensitive marine areas (dugong reserve, mangrove reserve and mariculture area) in the vicinity of the discharge point. Routine releases would elevate COD by more than 2 mg/l for a limited area of less than 15,000 m2 or a radius of less than 70m from the discharge point. The EIA conclud
ed that the impact of the mill’s routine and accidental COD release would be to slightly elevate COD in the mangrove reserve and dugong reserve but that the Class 1 seawater standard would be maintained in both areas, even in the event of the accidental discharge modeled.
P&B Mill – Emissions to Air
Air emissions of concern relate to emissions of combustion products from the power boiler, recovery boiler and lime kiln, emissions of dust from the lime kiln, VOCs arising from the BCTMP refiner and emissions of non condensable gases (NCGs) arising from the pulping process. NCGs contain several reduced sulfur compounds, which are the source of the unpleasant odors associated with kraft pulp mills. Control of each is now discussed.
Power Boiler Design
The power boiler is designed for steam conditions of 94 bar(g) and 475°C. Fuel input is approximately 200 MWth at design conditions, of which around 90% derived from coal and the remainder from various biomass sources The design adopted is a circulating fluidized bed, with addition of lime for control of SOx emissions. The boiler will also be equipped with selective non catalytic reduction (SNCR) for NOx control, and an electrostatic precipitator (ESP) for particulate (PM) emissions control. Point source emissions, of SO2, NOx and PM are expected to average below 200, 200 and 30 mg/Nm3 respectively, in all cases meeting local regulatory and WBG EHS Guideline values.
Recovery Boiler
The recovery boiler is designed for steam conditions of 94 bar(g) and 495°C. In accordance with BAT, black liquor is concentrated to 80% solids before entry to the recovery boiler, and the boiler itself has four levels of air feed for optimum combustion control and will be equipped with an ESP. Point source emissions, of SO2, NOx and PM are expected to average below 30, 200 and 30 mg/Nm3 respectively, in all cases meeting local regulatory and WBG EHS Guideline values.
Lime Kiln
The lime kiln, which will burn heavy fuel oil of up to 3% sulfur, will be equipped with low NOx burners and an ESP. Point source emissions, of SO2, NOx and PM are expected to be below 300, 400 and 50 mg/Nm3 respectively, in all cases meeting local regulatory and WBG EHS Guideline values.
BCTMP Refiner
Steam arising from the BCTMP refiner is directed to the heat recovery unit, and condenser, and passes through a scrubber before venting to atmosphere.
Non Condensable Gases Control
Odorous non-condensable gases include hydrogen sulfide (H2S), dimethyl mercaptan, and dimethyl sulfide, are collectively referred to as Total Reduced Sulfur (TRS) compounds and can be considered in the following categories:
Concentrated non-condensable gases (CNCGs), are low volume high concentration gases, also referred to as LVHC gases;
Dilute non-condensable gases,(DNCGs), typically high volume low concentration (HVLC) gases;
Dissolving tank vent gases (DTVGs), emitted from the recovery boiler dissolving tank vent, and with intermediat
e concentration;
TRS within recovery boiler and lime kiln flue gases,
Diffuse source.
CNCGs will be collected from relevant sources, i.e.: the heavy black liquor storage tank, methanol production system, evaporation vacuum system, foul condensate tank. These CNCGs are then transported to the main destruction system, which is a dedicated CNCG burner within the recovery boiler. If this CNCG destruction system is unavailable, the CNCGs will instead be routed without venting to the first backup system, a nozzle in the power boiler, and if both are unavailable CNCGs would be routed without venting to a second backup system, a flare on the recovery boiler roof. In the unlikely event that none of these three CNCG destruction systems is available, CNCGs would be vented to atmosphere, from the recovery boiler building roof, at a height of greater than 65m above ground. This design, with a main and two backup CNCG destruction systems meets BAT.
DNCGs will be collected from the chip digester, several vents in the fiber line, the recovery boiler vent tank, evaporation plant vents and causticizing plant vents. After pre-treatment such as washing and/or cooling, gases are reheated and sent to the DNCG destruction system. The primary DNCG destruction system is the recovery boiler, where DNCGs are mixed with dissolving tank vent gases and air and supplied as secondary combustion air to the recovery boiler. There is a single back up destruction system, the power boiler, while if both systems are unavailable, DNCGs would be vented to the stack on the recovery boiler building roof.
Flue gases from the recovery boiler and lime kiln will be discharged approximately 120 m above ground. Only limited unburnt TRS in the recovery boiler stack is expected due to the boiler design which overtly requires NCG destruction and combustion control which will include continuous monitoring of TRS, among other compounds, in the flue gas. Lime kiln emissions will be limited by appropriate system design, high quality lime-mud washing, and continuous monitoring and adjustment of combustion conditions.
Diffuse TRS emissions sources are controlled in several ways. Process systems are sized to avoid spills due to upset conditions, while collection sumps are connected to the NCG collection system. Potential emissions from the effluent treatment plant will be controlled by control of the pH of neutralization basins ahead of the effluent treatment system.
P&B Mill - Ambient Air Quality
Combustion Products
The EIA reports analysis of dispersion of combustion products from the mill P&B project, and assesses the impact of the P&B Mill on the overall objective to maintain Chinese Class II air quality objectives, as defined by GB3095-1996. The EIA’s review is summarized in the sections that follow; however it should be noted that Stora Enso expects the project’s emissions to air to be less than the values used in the EIA. One reason for this is that in the time
since the EIA was completed the decision has been taken to add SNCR to the power boiler, in order to reduce expected NOx emission from 300 to 200 mg/Nm3, in response to the updated Chinese standard GB13233-2011.
Analysis was based upon a 200 x 200 m grid centered on the mill chimney, and also considered the impact of the project at seven sensitive points up to 10 km distant from the mill site. Maximum daily concentrations of SO2, NO2 and PM10 attributable to the mill were calculated to be 19.6%, 13.8% and 3.2% of the air quality objective respectively. At the seven points of concern, project impact plus pre-project baseline will cause the following proportion of the air quality standard to be observed: SO2 18% of the standard at Bingchi Village, of which the project contributes up to 3% of the standard: NO2, 16% of the standard at Yanduncun district of Tieshan Port, of which the project contributes 3% of the standard, and PM10, 57% of the standard at Xingang, of which the project contributes 1% of the standard, reflecting high PM10 in the baseline. It is concluded that the project will not have major impact on ambient concentration of combustion products, and that air quality objectives will be met.
Odor
The expected odor impact of the project was assessed by preparation of a model of H2S dispersion from the lime kiln and recovery boiler flues. The model assumed continuous emissions of 6 kg/hour of H2S which exceeds expected emissions, given the state of NCG controls described in the earlier section. Modeling showed a maximum H2S concentration of 6.5 µg/m3 at the Yandunchun area. This is within the Chinese air quality objective. However, modeling is believed to overstate the impacts. Modeling also shows H2S concentrations at five settlements, Beimu, Pokoutang, Xinwupo, Yaxi and Haishanba that exceed the Chinese air quality standard. These areas are scheduled for future conversion to industrial areas, for other users of the Tieshangang Industrial Zone.
Solid and Hazardous Waste Management
The project will seek to minimize waste production. Plant-based wastes, such as bark, wood residues and water treatment plant sludge will be burnt in the power boiler. Ash arising from the power boiler will be supplied to a cement company for use in blending cement. Other solid and hazardous wastes will be transported by a licensed contractor to a landfill built as part of the Tieshangang development.
Hazardous Materials Management
Stora Enso will develop appropriate controls for the safe management of hazardous material at the mill site before such materials are in use, and shall oversee the performance of construction contractors in this regard. A dual language (English and Chinese) safety manual, and safety standards for the project have already been developed.
In plantation operations, hazardous materials used are fuels and lubricants associated with the Company’s vehicle fleet operations and plantation equipment and agrochemicals used for site preparation and out-planting. The Company has established procedures for the operation and maintenance of its own equipment and provides written procedures for fuel storage and dispensing to contactors which are regularly reviewed in the field. Review of contractor compliance with the sustainability criteria indicates steady improvement in fueling practices, recovery of used oils, and safe storage at fuel depots.
The Company purchases and uses agrochemicals. Glyphosate (a herbicide) is used after harvest and before replanting to reduce understory growth and prevent fire. Herbicide is applied using backpack sprayers and is reapplied during the first two years until canopies close and reduce weed growth. Contractors are trained in proper application of herbicides and direct observation and review of contractor performance records indicate that appropriate personal protective equipment (PPE) is routinely available and used. Proper maintenance and calibration of spraying equipment remains an area for improvement to reduce exposure to overspray and unnecessary costs. Concentrated Glyphosate is mixed with water at field sites and empty containers are routinely collected and removed.
General soil surveys are conducted on a network of 160 permanent sample points to determine broad fertility and limiting factors. Mechanical pitting may be exacerbating soil fertility limitations on degraded sites and improved soil analysis will help reduce over fertilizing. A general prescription of manual liming (CaCO3) (for the planting of the first rotation) during pitting followed by application of a granulated composite (NPK) fertilizer during out planting is followed. Polymer gels are often included in the pits to extend available water.
A review of pesticides, herbicides and fertilizers stores and application equipment at each plantation and the central nursery indicated reasonable control of inventories management but the ability to control access in field operations is challenging. All fertilizers, pesticides and herbicides comply with IFC and FSC requirements and meet Chinese laws and internationally-recognized practices for proper storage, ventilation and availability of proper emergency information. MSDSs for each agrochemical used was available at the Beihai office but not at all regional offices or planting sites which should be corrected.