Reduction in GHG Emission by Clean Energy Alternatives

Development of effective GHG mitigation strategies requires a detailed understanding of the types of industries and their energy-use patterns and associated emissions. This has recently been made possible by the U.S. Environmental Protection Agency (EPA) Greenhouse Gas Reporting Program (GHGRP). Under the Mandatory Reporting of GHGs Rule, facilities with annual direct emissions greater than or equal to 25,000 metric tons carbon dioxide-equivalent (МТСО,е) are required to report to the EPA (Part98—Mandatory Greenhouse Gas Reporting 2016). Over 8,000 facilities representing nine industry sectors reported direct emissions of 3,200 million MTC0₂e (MMTC0₂e), or nearly half of U.S. total GHG emissions, for the 2014 reporting year [3-6].

NREL (National Renewable Energy Laboratory) selected fourteen key industries with the highest amount of GHG emissions and thermal heat duties. Within these industries, representative plants were selected to determine how clean heat from SMRs, SIPH, and geothermal sources could be used. The GHGRP data allowed further disaggregation of thermal energy use, enabling analysis by fuel type, combustion-unit type, and end-use for the 14 industries. The common feature of the target industries is that they convert raw materials into energy services by means of physical and chemical changes. These changes generally require thermal energy to affect solids and liquids heat-up, melting, and evaporation and to heat up reactants to initiate molecular bond-breaking and to sustain the propagation of chemical reactions. Heat demands range from low-temperature steam (50°C, 0.7 megapascal [MPa]) for steeping in corn wet-milling to high-temperature operations up to 2,200°C for electric arc furnaces. The scale of heat demand for the average facility ranges from 0.016 TJ/day (15 MMBtu/day; or 0.2 MWt) for electrochemical production of 1,330 tons per day chlorine to 26 TJ/day (25,000 MMBtu; or 300 MW) for 5,273 tons per day of potash, soda, or borate mining and processing.

The study [116] identified several technical challenges and opportunities to application of clean energy sources for industrial heat users including: (a) quality of heat required by the user (or temperature of the working fluid), (b) industry process heat- transfer modes, (c) scale of heat source versus heat user demand, which may be mitigated by selecting the appropriate source or by industrial clustering (viz., an energy park), (d) transport requirements between the heat source and industrial process-unit operations, which involves distance and the materials needed for that transport, (e) thermal energy storage needs and options, (f) hybrid heat/electricity production, (g) electrification of heating processes, and (h) hydrogen production and use as an intermediate energy source.

A summary of the findings of this study is given in Table 7.9. The study indicated that the largest end-uses of combustion energy in 2014 were CHP and/or cogeneration (37% of calculated energy use), conventional boiler use (32%), and process heating (24%). Natural gas was the most-used fuel by the target industries, accounting for 44% of calculated combustion energy use. The study also indicated that hybrid ther- mal/electricity generation may help balance hourly, daily, and/or seasonal electrical

‘ Includes C0₂ from biomass combustion.

“ SMR temperatures up to 850°C. SIPH temperatures up to 1,000°C, geothermal heat supply up to 150°C.

Industries with process temperatures above 1,000°C (i.e., lime and cement, iron and steel) were not addressed in the analysis estimating potential alternative heat supply, although the report discusses applicable alternatives. Likewise, industries that rely on their process byproducts for combustion fuels (i.e., pulp and paper, petrochemical manufacturing) were also excluded from the estimates of potential alternative heat supply.

cycles. Thermal energy storage concepts such as those being developed for concentrating solar systems may help coordinate grid profiles with industry heat use profiles. SMRs were identified as an option for process heat and hydrogen production for feedstock use.

HESs have been proposed as a solution to using the excess power generation capacity that exists on the electrical grid when the generation capacity exceeds demand periods. In the context of the national energy systems, the definition of a hybrid system is one that dynamically uses heat or electricity to optimize the financial efficiency of the systems by producing the highest value set of energy services and products throughout the year. These products include electricity, manufactured goods, and intermediate energy carriers that may be stored or directly used to produce the set of products. The value proposition of a “greenfield” HES concept is currently being addressed by DOE, with an emphasis on regional scenarios that include a relatively high, hypothetical penetration of renewable energy [2,116,117]. A “brownfield” HES at an industrial site would involve the addition of a thermal energy generation source that is dynamically connected to the grid. Three scenarios presented by Ruth et al. [116] provide a general view of the basic system integration possibilities for clean thermal energy and power generation.

The analysis by Ruth et al. [117] reveals that clean energy sources may economically displace with industry fossil-fired heat generation under the assumptions considered in the study; however, the value position of hybrid operations will depend on the value of electricity. The role and cost of energy storage will also drive hybrid system deployment and operation considerations. HES may connect to industry through energy storage and energy carriers that are produced using the excess power generation sources that are not tightly coupled to industry. Geographical separation, differences in SMR scales, and industrial operation cycles may be addressed with the production of an intermediate product. Potable water, hydrogen, and other intermediate chemicals such as methanol and ammonia are examples of intermediate products. Seasonal energy use patterns are an important consideration for HES. For example, agriculture residues may be processed into energy products during or following the summer-to-fall harvest season. This conveniently corresponds to the fall period when electricity demand is at the lowest level for the year. Similarly, ammonia production during the spring could take advantage of the excess electricity generation capacity while producing fertilizers needed for spring and summer agriculture demands. The trade-off of ammonia and fertilizer plant capacity factors and product storage associated with constant generation throughout the year should be taken into consideration in such cases.