KRES-ESTM revamp produces more ammonia from less natural gas by energy substitution Vikram Singh, Shashi Singh KBR
The 5th KRESTM technology based Ammonia Plant is now in operation in a grass-root project at P.T. Panca Amara Utama (PAU), Indonesia. This follows earlier successful operations in revamp projects - one since 2009 and another since 2015. KBR has therefore studied various schemes in which KRES technology could benefit ammonia plant operators. As a result, KBR is now offering low cost KRES-ESTM technology (patent pending) for revamping ammonia plants by energy substitution.
Ammonia plants having either expensive or curtailed/uncertain supply of natural gas may find this technology a solution to their problem if an alternative source of energy, e.g. coal, is available. It offers an ideal solution for locations facing natural gas shortage or where natural gas is likely to become too expensive to allow viable operations, after building the plant. This enjoys reliability of reforming process (over coal gasification). It also allows the plant to switch totally to natural gas in the future if natural gas becomes available. The revamped ammonia plant requires oxygen and steam imports. Steam import can be met by either using existing capacity or an alternative source of energy. Alternative source of energy may be fossil fuel like coal or other sources. Total natural gas consumption is reduced to less than 6.35 Gcal/MT of ammonia by adding a new reforming exchanger to the existing primary and secondary reformers.
Three examples of KRES-ES based revamps are presented including technical and economic analysis to illustrate the application of this technology.
Key words: KRESTM - KBR reforming exchanger system, ammonia plant, coal, natural gas, ammonia, energy saving.
Vietnam has a large range of domestic primary energy sources. These resources however are fast depleting. The power sector has grown in Vietnam as also the consumption of natural gas in the generation of power, thus leading to a competing use of natural gas for power generation versus downstream industry. This, along with the government’s continued thrust on implementation of energy efficiency measures in operating plants, gives an opportunity to the ammonia industry to consider technology options to address both these needs (a) use of alternate source of energy for ammonia production, e.g. coal and (b) implementing energy reduction measures in their plants.
KRESTM - KBR reforming exchanger system that replaces conventional primary and secondary reformers in an ammonia plant has been in successful commercial operation [1, 2] in the ammonia plants in Methanex, Canada, since 1994 and in Liaohe, China, since 2003. A reforming exchanger is the heart of the KRES technology. It uses high temperature process heat exiting the secondary reformer (or exiting an auto-thermal reformer) to produce syngas by reforming an additional flow of natural gas and steam. As described in a previous paper , KRES has been offered as two process schemes. One of these two schemes is used at Methanex and Liaohe. The other scheme is used in the third KRES unit in the Chambal Fertilizers & Chemicals Ltd Plant. Chambal Fertilizers & Chemicals Ltd. (CFCL) in India commissioned their KRES based revamp project in their ammonia plant-1 that is in successful operation since April 2009. Since then, two more plants have implemented KRES, one in PCS Lima Plant in Ohio (US) in 2015 (Foster Wheeler Technology) and another in the 1,900 million ton per day grassroot KBR technology ammonia plant in P.T. Panca Amara Utama (PAU), Banggai, Indonesia in 2018.
Table 1. CFCL performance summary
KBR is now offering KRES-Energy Substitution (KRES- ESTM) technology (patent pending) as another application of KRES for revamping ammonia plants. This technology provides a low-cost revamp solution to any existing ammonia plant that has either an expensive, curtailed and/ or uncertain supply of natural gas but has an alternative source of energy available. The revamped ammonia plant requires oxygen and steam imports. Steam import can be met by using either existing or new capacity. The source of energy for steam could be fossil fuel (e.g. coal) or another non-fossil energy source.
Total natural gas consumption is reduced to less than 6.35 Gcal/MT of ammonia by adding a new reforming exchanger to the existing primary and secondary reformers. This technology can be used to dramatically reducethedependenceonnaturalgaswhileeitherkeeping the same ammonia production capacity or increasing it. Three examples of KRES-ES based revamps are presented in this paper with their technical and economic analysis to illustrate the application of this technology.
2. CFCL revamp project
CFCL operates two ammonia plants in Gadepan, India. The first plant having a 1,500 ton per day design capacity, based on Haldor Topsoe technology, was commissioned in 1994. In 2005, CFCL decided to revamp this plant to increase its capacity and improve energy efficiency and therefore awarded revamp studies to both, Haldor Topsoe, the technology provider of the original plant, and KBR. After comparing the revamp process technologies offered by both parties, CFCL decided to implement the revamp project using KBR technology, including KRES as its key feature, as it provided better energy efficiency as well as better operability.
From 2006 to 2008, the revamp project went through its basic and detailed engineering, procurement and construction. The project had been divided into two phases; and stage-1 was successfully commissioned in April 2009. Stage-1 includes KRES, a synthesis loop upgrade plus other miscellaneous items. After implementing the full revamp changes, KRES application will increase syngas generation capacity by more than 30%. The loss of ISBL steam generation per ton of ammonia due to KRES is offset by improved heat recovery as well as by reducing the ISBL energy consumption. Thus the energy efficiency of the ammonia plant is improved as summarised in Table 1.
The prior conventional reforming system of primary and secondary reformers has been upgraded with KRES consisting of the existing primary reformer, a secondary reformer and the reforming exchanger. KRES in operation in the CFCL ammonia plant since April 2009 is shown in Figure 1. The CFCL reforming exchanger, a compact piece of equipment, is located in front of the large side fired reformer furnace. The reforming exchanger effluent flows to the inlet of the existing reformed gas waste heat boiler. It contributes more than 30% of the syn-gas generation capacity. Besides contributing to capacity and efficiency improvement of the ammonia plant, it has improved the performance of the old reformed gas waste heat boiler by reducing its inlet temperature and thus its thermal and mechanical stresses. Boiler outlet temperature is lower so it improves the HT shift converter conditions. Operating conditions of the primary reformer are also milder as radiant duty is reduced.
3. KRES-ESTM process scheme
The KRES-ES process is configured to enable all ammonia plants to reduce their dependence on natural gas requirement by adding minimum equipment to provide a low-cost revamp technology solution. Ammonia plants having one or more of the following problems in the supply of their natural gas feed-stock can benefit from this technology: expensive, uncertain supply in the future, erratic or curtailed. Due to high product demand, some owners also need to increase their plant capacity but are hesitant due to lack of long term natural gas supply commitments. Ammonia plants in some countries are also looking for revamp options to reduce their CO2 emissions and carbon footprint.
Figure 1. KRES in operation in CFCL ammonia plant.
Figure 2. Ammonia Plant before revamp.
KRES-ES process technology provides the right solution to all such ammonia plant owners, provided a suitable alternative source of energy is available to owners to enable the “Energy Substitution (ES)” function to reduce use of natural gas.
Existing ammonia plants with a conventional reforming system have a primary reformer furnace followed by a secondary reformer to produce synthesis gas as shown in Figure 2. All such conventional plants can be revamped by upgrading their reforming system to KRES-ES as conceptually shown in Figure 3. A reforming exchanger will be tied in between the secondary reformer and the reformed gas waste heat boiler. A portion of the feed natural gas and steam mixture is fed to the reforming exchanger having conventional nickel based catalyst in its tubes where syngas is produced using high grade process waste heat.
Comparing the two schemes on equal syngas production basis as shown in Figures 2 and 3, heat duty on the existing primary reformer is reduced to about one third of that in the conventional existing system (Figure 2). Fuel gas consumption is significantly reduced. The existing furnace is reconfigured to a “Lite Reformer” by making minor mechanical changes. Imported oxygen is mixed with process air - to make enriched air with about 30 mol% O2 which is fed to the secondary reformer to complete the revamped system.
Figure 3. Ammonia Plant after revamp.
Table 2. Comparison of parameters before and after revamp
Substitute energy (to replace natural gas) can be from any source that can provide steam to the ISBL ammonia plant to meet the shortfall created due to the reduced duty of the reformed gas waste heat boiler. For example, a coal or pet coke fired boiler can be used to accomplish this or surplus steam from a power plant using non-fossil fuel may be used. A supply of oxygen is also required to enrich the process air. Oxygen can be drawn from a close-by plant or from an existing pipeline network, if available or produced in new oxygen package unit using alternative source of energy. Process steam import requirement will depend on how much heat load of the HP Boiler is being used for meeting reforming reaction’s endothermic heat requirement in the KRES unit. However, steam import can be reduced by switching some turbine drivers to electric drivers or by improving ISBL waste heat recovery or by reducing ISBL process heat consumption in the CO2 removal system. Depending upon the conditions of the existing plant, it may be possible to avoid or significantly minimise the requirement of import steam by using suitable heat integration.
In most cases, the natural gas consumption of the ammonia plant is reduced to below 6.35 Gcal/MT of ammonia from present natural gas consumption of 7.3 to 9.5 plus Gcal/MT irrespective of the technology of the current plant and its furnace type. However, the total energy (natural gas plus the substitute source) consumption may or may not be reduced.
4. Low-severity equipment duty
KRES-ES has additional advantages as it reduces operating parameter severity which leads to improved mechanical reliability of the existing equipment post revamp. Operating conditions of both (a) primary reformer furnace and (b) reformed gas waste heat boiler become very mild post revamp, and typical benefits are identified in Table 2. Thus plants requiring maintenance/ replacements in these two critical and expensive pieces of equipment may expedite implementation of their KRES- ES based revamp to avoid such expensive repair and/or equipment replacement including a furnace re-harp.
5. Increased CO2 availability
In most cases KRES-ES produces sufficient CO2 by- product that is adequate to convert all the NH3 production to urea. This is very valuable to plants that can sell only urea (no ammonia) and have a CO2 shortfall, since surplus syngas need not be diverted to fuel or an expensive fluegas CO2 recovery unit is not required for production of additional CO2.
6. Revamp examples
Examples of ammonia plant revamps help illustrate how incorporating KRES-ES technology in the revamp flowsheet reduces the dependence on natural gas supply. It significantly improves the economics of the whole operation with or without a capacity increase of the plant. Here are three examples based on KBR studies and projects.
*Loss of capacity utilisation due to other factors (than natural gas curtailment) is excluded for clarity. Costs of natural gas and coal are USD 4.0 and USD 2.0 per MMBTU respectively. Ammonia sale price at the gate is USD 250 per metric ton. **Savings made by avoiding reharp of the reformer furnace and a RG-WHB maintenance is not considered in payback. ***Benefit of additional CO2 is not considered in payback.
Table 3. Key features of revamp example 1
*Loss of capacity utilisation due to other factors (than natural gas curtailment) is excluded for clarity. Costs of natural gas and coal are USD 4.0 and USD 2.0 per MMBTU respectively. Ammonia sale price at the gate is USD 250 per metric ton. **Savings made by avoiding reharp of the reformer furnace and RG-WHB maintenance is not considered in payback. ***Benefit of additional CO2 is not considered in payback.
Table 4. Key features of revamp example 2
6.1. Example 1: Improved capacity utilisation
This example describes a revamp where the plant has curtailed and erratic supply of natural gas. Natural gas curtailment is greater in winter when more gas is diverted by the supplier to higher priority users. The plant operates at capacities as low as 70% throughputs in winter and annual average capacity utilisation is only 85% for this 1,200 metric ton per day capacity plant. The increased capacity of over 1,200 metric tons per day is not required so the plant is revamped using the KRES-ES scheme (Figure 3) to reduce its dependence on natural gas and thus enabling it to operate at 1,200 metric ton per day capacity throughout the year even as gas supply is curtailed by up to 30%. Key features of this revamp case are summarised in Table 3.
6.2. Example 2: Revamped to increase plant capacity
This example describes a revamp where the plant has curtailed and erratic supply of natural gas as well as a robust market demand for ammonia.The plant operates atreduced throughputs, especially in winter. The owner is expecting a new natural gas supply contract but is concerned that the plant may be caught with curtailments in long term after spending on the capacity increase revamp project.
The revamp project is implemented to increase capacity to 1,500 metric tons per day from the present 1,200 metric tons per day using KRES-ES scheme (Figure 3). Besides revamping of the reforming system to KRES-ES, other parts of the plants are also modified to accommodate the increased throughput. Total natural gas consumption is 12% lower even at 1,500 metric ton per day production than what it was before the revamp and the plant will operate at 1,500 metric ton per day capacity throughout the year even as gas supply is curtailed. Key features of this revamp case are summarised in Table 4.
6.3 Example 3: CO2 emission reduction
This example describes a revamp where the plant must reduce its CO2 emissions significantly to meet new regulations. Revamping this vintage plant to improve its energy efficiency to the level of a new plant in order to reduce CO2 emission is cost prohibitive. KRES-ES is incorporated to reduce consumption of natural gas of the ammonia plant to 6.35 Gcal/MT. The ISBL ammonia plant requires HP steam import as well as O2 from OSBL. Both of these requirements are met by sourcing suitable quality of steam from a nearby power plant that uses non-fossil fuel as the source of energy. The oxygen plant drives its air compressor using this imported steam or alternatively it can use electric power supplied by the same power plant. Feasibility of sourcing the steam to OSBL of ammonia plant from such a non-fossil fuel based power plant needs to be confirmed for specific location. Key features are summarised in Table 5.
*Incremental CO2 by product flow is excluded from the quoted emissions; since it is either used in the urea plant or recovered as a product. Note: Savings made by avoiding reharping of the reformer furnace and RG-WHB maintenance is not considered in payback.
Table 5. Key features of revamp example 3
Table 6. KRES-ES revamp example summary
KRES-ESTM technology provides an economical revamp solution to any existing ammonia plant that is suffering from either expensive or curtailed and uncertain supply of natural gas but has an alternative source available for energy substitution (ES). It also has potential application for reducing ISBL ammonia plant’s CO2 emission or carbon footprint for countries where such regulation is enforced. The revamp examples illustrate that KRES-ES can be used to provide a customised revamp flowsheet to all ammonia plants that can benefit from energy substitution as summarised in Table 6.
Cost of revamp would depend on the extent of modification required in the flowsheet including other constraints which the plant has to incorporate in those changes, eg. steam balance, air compressor capacity and reformer furnace constraints.
1. X.Shen, X.Xu, W.Feng, S.Singh, A.Malhotra. Largest KRES reformer in service in China. Nitrogen and Methanol. 2005; 274: p. 39 - 46.
2. Avinash Malhotra, Paul Kramer, Shashi Singh. Revamp of Liaohe’s ammonia plant with KRES technology to reduce natural gas usage. AIChE Ammonia Safety Symposium, Denver, USA. 2004.
3. S.Singh, A.Jing. KRES technology makes ammonia plant revamping viable. GazChem 2007, Trinidad & Tobago. 2007.
4. Danish Energy Agency. Vietnam energy outlook report. 2017.
5. Upendra Singh, Shashi Singh, Avinash Malhotra. Successful operating experience of CFCL ammonia plant revamped with KBR KRES™ technology. Ammonia Technical Manual. 2011.
6. Timothy Kearns, Kim Taniguchi, Akhil Nahar, Tim Rembold. Successful project execution and commissioning of largest capacity KRES™ ammonia unit. AICHE 2016.